Re: 1978 merc 115 hp oil leaking
Holes near the top of the mid section rear are called "exhaust relief" and their purpose is to allow starting/idle/low speed exhaust gasses to exit into the air rather than be forced out the hub which causes back pressure and works against you in the conditions mentioned.
Agree on source of oil. Agree on using highest quality oil (I use Merc top of the line). Agree on don't worry about it. I used to trim the engine up a few degrees to insure that oil couldn't puddle at the back of the cylinder (where the plug is). For years Merc built a line of small fishing motors built just this way for just that reason......the design included slanting the midsection to the rear which helped the lower unit to slide over submerged objects.
I don't think the '78 had a thermostat so the engine ran cold while trolling and this too contributes to condensation in the exhaust which, when mixed with the oil, makes it chocolate colored.
Usually, after I had trolled for awhile, I would pull in the gear, get up and on plane for a few minutes (until the smoke cleared out of the engine) and then back to trolling.
On the white part of what you found in the lower unit, that (you know) is water. Don't know when was the last time you changed it, but if it was recently, looks like you may have a leak down there. Best to use new blue washers on the screws any time you take them out; cheap insurance.
Mark
