Welcome blankcanvas,
I'm afraid that you're NOT going to like what I have to say so let's hope I'm wrong. Often am.
In the link below is the seal racerone mentioned. Item #14.
The bad news comes from several directions....
...If that cover (item 13).is leaking, replacing that seal probably won't stop the leak.
That is because that cover warps from heat and a new seal won't compensate for the warpage. It's burned many a pro tech trying to stop the bleeding.
My guess is that the goopy stuff is some sort of sealer somebody before you used to try to seal it up.
As you can see from the parts price list, that cover is not available and it hasn't been for a very long time. Although, I have not checked with yumbo.com
a parts place in Japan that might still have them.
Also, to remove and reinstall that cover you have to remove the powerhead from the oil case. Not a real difficult job but a real pain. Especially if it still leaks afterwards.
If you go there, you will need a new oil case to block gasket and the little "nestled" water passage oring. I also recommend a new exhaust pipe gasket as they blow out and cause problems. It's also a good idea to replace the water grommet at the top of the water supply tube while you're at it.
AND...
DON'T FORGET THE HIDDEN BOLT! or you'll bust the $1200 oil case!
So, what to do if you can't find a replacement cover?
I have only thought about doing this so I'm not sure that it would work so take my words with a big BLOCK of salt!
Here's what I might try.....
Use a high watt heat gun to
Carefully (it's made out of some kind of plastic) heat the cover up and then press it against a flat surface and hold it down until it cools.
I have considered a thick piece of glass to press it against might work well but anything that's flat and that will take the heat would work.
I would then fabricate a steel frame to go around the outer edge of the cover. It should be wide enough to allow for drilling the bolt holes and thick enough to prevent any warping. I think 1/8" might be adequate but the thicker the better....as long as there's clearance.
Then, just use slightly longer bolts to re-install it on the engine.
Because, if you just heat the cover up, flatten it out, then put it back, it will probably just warp again.
Then you're back to ■1.
Like I said, I hope I'm wrong about the whole thing but it may be what you're looking at there.
The bright side would be that having the powerhead off gives you the opportunity to clean out the oil sump and screen. I would also check the crank, rod and thrust bearings for wear as I believe those are still available. If you like the outboard and plan on keeping it long, doing those things and checking the oil pump clearnces would ensure trouble free service for years to come.
These are some truly GREAT old units but new parts will only be harder to find as time goes on.
I did see that yumbo does carry a replacement carb for some of them though. Something you can't get here in the States.
Wishing you the best of luck.
