Don't know if this helps,
I had a film of heavy duty oil in bilge. But engine is an 84 and everything is original and old . Engine also has a slight oil leak
Power wash and de grease the bilge often
This season had lower unit impeller pump changed and gear oil was topped off
Thinking why do I have so much oil in bilge but just chalked it up too old boat & engine
After 1/2 doz short fishing trips I checked gear oil in lower unit.
Was surprised it was loaded with water , not milky oil all water
I was lucky did no damage,
Took boat too a mom & pop shop here in Orlando seems a number of seals
in upper part of lower unit was causing gear oil too dump into bilge