I bought a little 17 foot runabout with a 4.3 merc I/O. I tested the motor and outdrive with motor muffs and everything ran fine. So I take it to the lake the next day and run about half a tank of gas through it and it performs well. I load the boat back on the trailer, take it home and the next...
If your water pressure is too high when using motor muffs could that cause a gear oil leak?
I read in the manual to be wary of high water pressure when using muffs. It was right after running motor with muffs that I found gear lube in the bilge...