Re: Oil fill top of Sterndrive?
If you pulled the big slot head screw with the diptstick on it, that is the upper gearcase. There will be an actual drain/fill plug for that gearcase, midway down on the right side of the case, forward of the upper gearcase shroud. Sounds like you might have had some water intrusion. Drain it, refill it, run it and recheck it. If it does not milk up quickly, just run it a few times (in the water) and keep an eye on it. Who knows how long it has been since it was changed.
Keep in mind for both upper and lower, they use the same oil and you FILL them from each of their BOTTOM plugs. Also check the oil in the intermediate housing. You should be able to see oil in the opening when you pull the plug. If you do not see any, I would drain it and refill it with the same oil. For the IH, you fill it from it's top inspection plug.
There are other lube points that need attention, also.
