{"product_id":"sierra-18-0523-oil-seal-for-mercury-mercruiser","title":"Sierra 18-0523 Oil Seal for Mercury \u0026 MerCruiser","description":"\u003cp class=\"nvn-hero\"\u003eThe Sierra 18-0523 is a replacement oil seal for Mercury outboards and MerCruiser sterndrives. It keeps gear lube in and water out at a rotating shaft, sized 2.132 in OD by 1.640 in shaft by 0.282 in thick. It meets or exceeds the OEM part and cross-references Mercury 26-43993.\u003c\/p\u003e\n\n\u003cdiv class=\"nvn-description\"\u003e\n\u003cp\u003eThe Sierra 18-0523 is a replacement oil seal built for Mercury outboards and MerCruiser sterndrives. It's a small part that does a big job. This seal rides against a rotating shaft and keeps your gear lube where it belongs, inside the housing, while it keeps water and grit on the outside. When a seal like this gives up, you'll usually know it by the lube. Either it's weeping out and leaving a slick, or water has worked its way in and turned the oil a milky gray. Neither one is good, and neither one fixes itself.\u003c\/p\u003e\n\u003cp\u003eSierra builds this seal to meet or exceed the original equipment part it replaces, so you're not giving up anything by going with it. It cross-references to Mercury 26-43993 and GLM 85090, which makes it easy to confirm you've got the right piece before you order. The dimensions are what matter most here. Outer diameter is 2.132 inches, the shaft bore is 1.640 inches, and the seal is 0.282 inches thick. Those three numbers have to match the seal you're pulling out. Get one of them wrong and it either won't seat in the bore or it won't seal against the shaft.\u003c\/p\u003e\n\u003cp\u003eWhere does a seal like this live? On a Mercury or MerCruiser drive, oil seals sit at the points where a spinning shaft passes through a stationary housing, in the gearcase and around the drive assembly. That's a high-wear spot. The shaft turns every second the engine runs, and the seal lip is in constant contact. Add salt, sand, and fishing line, and it's easy to see why these are wear items. A leaking gearcase seal doesn't just make a mess. Left alone, water in the gear lube leads to corrosion and pitting on the gears and bearings, and that turns a small part into a big repair bill. Most techs replace seals as a matter of course whenever the lower unit or drive is apart for other work. It's cheap insurance against pulling the whole thing back down a month later.\u003c\/p\u003e\n\u003cp\u003eIf you're doing your own service, a few things are worth knowing. The seal presses into its bore, and you want it going in square, not cocked. A proper seal driver or a socket that matches the outer diameter saves you a lot of grief here. Pay attention to which way the lip faces. The lip points toward the fluid it's holding back, and installing it backward is one of the most common reasons a fresh seal leaks. A light film of gear lube on the lip during assembly helps it slide onto the shaft without tearing. Take your time and it goes in clean.\u003c\/p\u003e\n\u003cp\u003eWho's this for? Anybody keeping a Mercury outboard or a MerCruiser sterndrive running right. If you're doing an annual lower unit service, chasing a lube leak, or rebuilding a gearcase, matching the seal by these dimensions and the cross-reference numbers is the way to go. And if you're not sure this is the exact seal your drive needs, check the number on the old seal or your parts diagram against the 26-43993 or 85090 reference before you buy. A seal is a couple of dollars. Doing the job twice is what costs you.\u003c\/p\u003e\n\u003cp\u003eOne honest note. This is a single oil seal, sold on its own. It's not a full seal kit and it doesn't include shims, O-rings, or a water pump kit. If you're doing a complete lower unit reseal, you'll want to line up the rest of those parts separately. But for replacing this specific seal, matched by size and cross-reference, the Sierra 18-0523 does exactly what it's supposed to and nothing you don't need.\u003c\/p\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eKey Features\u003c\/h2\u003e\n\u003cul class=\"nvn-features\"\u003e\n  \u003cli\u003eSized 2.132 in outer diameter, 1.640 in shaft bore, and 0.282 in thick, match these three to the seal you're replacing\u003c\/li\u003e\n  \u003cli\u003eFits Mercury Marine outboards and MerCruiser sterndrives at rotating-shaft seal points in the drive and gearcase\u003c\/li\u003e\n  \u003cli\u003eCross-references Mercury 26-43993 and GLM 85090 for quick, confident ordering\u003c\/li\u003e\n  \u003cli\u003eMeets or exceeds the OEM part it replaces, so sealing performance holds up over a full season\u003c\/li\u003e\n  \u003cli\u003ePresses into a standard seal bore, install with a seal driver or matching socket for a square, leak-free seat\u003c\/li\u003e\n  \u003cli\u003eSold as a single oil seal, the right call when you just need to replace this one part\u003c\/li\u003e\n  \u003cli\u003eEngineered for the harsh marine environment to Sierra's marine build standard\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cdiv class=\"nvn-trust\"\u003e\n  \u003ch2\u003eWhy Buy from NVN Marine\u003c\/h2\u003e\n  \u003cul\u003e\n    \u003cli\u003eAuthorized Sierra Marine reseller, full manufacturer warranty\u003c\/li\u003e\n    \u003cli\u003eNMEA member and ABYC certified, advice from real boat techs\u003c\/li\u003e\n    \u003cli\u003eSame-day shipping before 3 PM ET on in-stock items\u003c\/li\u003e\n    \u003cli\u003eNY headquarters and Fort Lauderdale flagship retail store\u003c\/li\u003e\n  \u003c\/ul\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\n\u003cdiv class=\"nvn-faq\"\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhat does the Sierra 18-0523 oil seal fit?\u003c\/summary\u003e\n    \u003cp\u003eIt's a replacement seal for Mercury Marine outboards and MerCruiser sterndrives. It fits at rotating-shaft seal points in the drive and gearcase. Confirm fitment by matching the dimensions or by cross-referencing your part number.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhat are the exact dimensions?\u003c\/summary\u003e\n    \u003cp\u003eOuter diameter is 2.132 inches, the shaft bore (inner diameter) is 1.640 inches, and the seal is 0.282 inches thick. All three need to match the seal you're replacing.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhat Mercury part number does this replace?\u003c\/summary\u003e\n    \u003cp\u003eIt cross-references Mercury 26-43993. It also interchanges with GLM 85090. Check the number on your old seal or your parts diagram against those references before ordering.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eIs this a genuine Mercury part?\u003c\/summary\u003e\n    \u003cp\u003eNo. It's a Sierra replacement seal, not an OEM Mercury part. Sierra builds it to meet or exceed the original equipment part it replaces, and it cross-references the Mercury number so you get the same fit.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eHow do I know it's the right seal for my drive?\u003c\/summary\u003e\n    \u003cp\u003eMatch the three dimensions to the seal you're pulling out, or cross-reference by Mercury 26-43993 or GLM 85090. If any of those line up, you've got the right piece. If you're unsure, check your engine's parts diagram first.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhen should I replace an oil seal like this?\u003c\/summary\u003e\n    \u003cp\u003eReplace it if you see gear lube weeping out, or if your lube comes out milky or gray, which means water is getting in. Most techs also swap seals as routine whenever the lower unit or drive is apart for other service.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eDo I need special tools to install it?\u003c\/summary\u003e\n    \u003cp\u003eA seal driver or a socket matched to the outer diameter helps press it in square without cocking it. Note which way the lip faces, it points toward the fluid it holds back, and a light film of gear lube on the lip helps it slide on without tearing.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eDoes it come with anything else, like a seal kit?\u003c\/summary\u003e\n    \u003cp\u003eNo. This is a single oil seal, sold on its own. It doesn't include shims, O-rings, or a water pump kit. For a complete lower unit reseal, line up those other parts separately.\u003c\/p\u003e\n  \u003c\/details\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eTechnical Specifications\u003c\/h2\u003e\n\u003ctable class=\"nvn-specs\"\u003e\n  \u003ctbody\u003e\n    \u003ctr\u003e\n\u003cth\u003eTitle\u003c\/th\u003e\n\u003ctd\u003eSierra 18-0523 Oil Seal for Mercury Outboard \u0026amp; MerCruiser Sterndrive\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eBrand\u003c\/th\u003e\n\u003ctd\u003eSierra Marine\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eManufacturer Part Number\u003c\/th\u003e\n\u003ctd\u003e18-0523\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eUPC\u003c\/th\u003e\n\u003ctd\u003e030999874351\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003ePart Type\u003c\/th\u003e\n\u003ctd\u003eOil Seal\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eApplication\u003c\/th\u003e\n\u003ctd\u003eMercury Marine Outboard \/ MerCruiser Stern Drive\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eOuter Diameter\u003c\/th\u003e\n\u003ctd\u003e2.132 in\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eShaft Size (Inner Diameter)\u003c\/th\u003e\n\u003ctd\u003e1.640 in\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eThickness\u003c\/th\u003e\n\u003ctd\u003e0.282 in\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eMercury Cross-Reference\u003c\/th\u003e\n\u003ctd\u003e26-43993\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eGLM Cross-Reference\u003c\/th\u003e\n\u003ctd\u003e85090\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eQuality Standard\u003c\/th\u003e\n\u003ctd\u003eMeets or exceeds OEM part it replaces\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003cscript type=\"application\/ld+json\"\u003e\n{\n    \"@context\": \"https:\/\/schema.org\",\n    \"@type\": \"FAQPage\",\n    \"mainEntity\": [\n        {\n            \"@type\": \"Question\",\n            \"name\": \"What does the Sierra 18-0523 oil seal fit?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"It's a replacement seal for Mercury Marine outboards and MerCruiser sterndrives. It fits at rotating-shaft seal points in the drive and gearcase. Confirm fitment by matching the dimensions or by cross-referencing your part number.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"What are the exact dimensions?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"Outer diameter is 2.132 inches, the shaft bore (inner diameter) is 1.640 inches, and the seal is 0.282 inches thick. All three need to match the seal you're replacing.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"What Mercury part number does this replace?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"It cross-references Mercury 26-43993. It also interchanges with GLM 85090. Check the number on your old seal or your parts diagram against those references before ordering.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Is this a genuine Mercury part?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"No. It's a Sierra replacement seal, not an OEM Mercury part. Sierra builds it to meet or exceed the original equipment part it replaces, and it cross-references the Mercury number so you get the same fit.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"How do I know it's the right seal for my drive?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"Match the three dimensions to the seal you're pulling out, or cross-reference by Mercury 26-43993 or GLM 85090. If any of those line up, you've got the right piece. If you're unsure, check your engine's parts diagram first.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"When should I replace an oil seal like this?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"Replace it if you see gear lube weeping out, or if your lube comes out milky or gray, which means water is getting in. Most techs also swap seals as routine whenever the lower unit or drive is apart for other service.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Do I need special tools to install it?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"A seal driver or a socket matched to the outer diameter helps press it in square without cocking it. Note which way the lip faces, it points toward the fluid it holds back, and a light film of gear lube on the lip helps it slide on without tearing.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Does it come with anything else, like a seal kit?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"No. This is a single oil seal, sold on its own. It doesn't include shims, O-rings, or a water pump kit. For a complete lower unit reseal, line up those other parts separately.\"\n            }\n        }\n    ]\n}\n\u003c\/script\u003e\n","brand":"Sierra Marine","offers":[{"title":"Default Title","offer_id":45080744820829,"sku":"2010104","price":19.59,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0299\/7266\/0317\/files\/ImageServerAPI_e262aa08-de54-4496-a34d-ac87768e4ff9.jpg?v=1789996037","url":"https:\/\/nvnmarine.com\/products\/sierra-18-0523-oil-seal-for-mercury-mercruiser","provider":"NVN Marine","version":"1.0","type":"link"}