Mercury outboard 65 hp est. mid-1970's. I'm fairly new to working on outboards, but mechanically inclined. Trying to change LU gear oil, the marina guy said to use "flush" screw to pump in new oil while "vent" screw open. No old oil can out of the flush hole, and only got in about a third of the new gear oil. Closed the screws and later noticed oil leaking from the propeller, as well as from the water intake screens. First of all, how to get more gear oil in, and secondly, what has caused the leaks? What is the suggested repairs? Thanks.