Re: 1976 sterndrive?
outdrives have lots of anti friction bearings, and lots of places for metallic wear particles to hide.
You can run/change/run the oil several times, but with no filter and gravity working against you, its always possible some metal particle will take the bearings out underway. You might get lucky for a few seasons too. always a judgement call that only the owner can make
to do it right, best to disassemble a drive and clean all the parts with solvent and rebearing/ reseal / reassemble
with shiny, metallic oil, your bearing rollers and races will be spalled and headed for failure