I have a 1989 merc 90hp outboard with a blown cylinder. By a stroke of luck I found a replacement motor that was cheaper than having my powerhead rebuilt. I replaced it with a 1990 90hp mariner motor. The new motor runs get but it is not in as good shape as far as upkeep as my old one (corrosion, lube, etc.). I now have developed a small lower unit leak. A small amount of lube leaked from the intake. The lube was milky indicating water intrusion right? Can I switch out the two lower units? Are they compatible? I think they are. Is it adviseable?
hope this helps