Sierra 18-2681 Lower Unit Seal Kit | Johnson Evinrude 6HP

The Sierra 18-2681 is the complete seal kit for resealing the lower unit on a Johnson or Evinrude 6 HP outboard built between 1968 and 1979. If you've pulled the gearcase drain plug and watched milky, coffee-colored oil run out, water is getting past a tired seal. That's exactly what this kit fixes. Everything that seals the gearcase on these little two-strokes is in the box, so you can do the job right the first time instead of chasing one leak at a time.

Fitment matters here, so read this part twice. The kit covers the 6 HP motors from 1969 through 1979 without fuss. The 1968 model year is the one to watch. It only fits the 1968 motors carrying the A or R suffix in the model number. The factory changed the housing and the bearing bore depth on other 1968 variants, and a mismatched case ends up with the wrong O-ring stack and seals that won't seat. Check the suffix stamped on your engine's model tag before you order. Get that right and the rest of the job is straightforward.

Here's what you get. The oil seals that keep gear oil in and lake water out. The O-rings that seal the shaft bores and the plug threads. The spaghetti seal that runs the split line where the two halves of the gearcase meet. The bearing housing gasket for the bearing carrier. And the drain and fill plug washers. That last item sounds minor, but a flattened old plug washer is one of the most common reasons a freshly sealed lower unit weeps oil on the very first run.

A few notes from doing these jobs. The spaghetti seal is the fussy part. It's a thin bead of rubber that rides in the groove around the gearcase mating surface, and it wants to shred or roll if you rush it. Pack the groove with a good gasket grease, lay the seal in, and work it around slowly with steady pressure so it seats without twisting. Take your time and it goes in clean.

While the lower unit is apart, look hard at the bearings and races. New seals riding on a pitted or rough race won't last, sometimes not even ten hours of run time before they start passing water again. If the races show pitting or the bearings feel notchy, replace them now while everything's on the bench. It's cheap insurance compared to splitting the case a second time next season.

The bearing housing gasket occasionally needs a light trim to clear casting flash on some of the 1970s 6 HP cases. Test-fit it dry, and if it hangs up on a rough spot in the casting, trim it back a hair rather than forcing it. When you button the bearing carrier and lower housing back together, snug the fasteners down in three even steps, working around the pattern. Cranking one bolt fully before the others is how a lower oil seal gets pushed out of its bore, and then you're right back where you started.

Two more things that save headaches. Use the fresh plug washers from the kit, and if you want the cleanest possible seal, annealed copper washers seat best and won't leak on the first heat cycle. And when you refill, use a marine-grade hypoid gear oil rated for outboard lower units. Skip the automotive gear oils. They foam under the load and heat of an outboard gearcase and can push oil right past the seals you just installed.

Bottom line, this is the right kit for keeping a vintage 6 HP kicker alive and dry. These old motors are simple, tough, and worth maintaining, and a proper reseal every few seasons is the single best thing you can do for the lower unit. Sierra builds this kit to meet or exceed the original equipment part it replaces, so you're not giving anything up by going aftermarket. Order by Sierra part number 18-2681, confirm your 1968 suffix if that's your year, and you'll have everything you need to send that gearcase back out watertight.