Re: lower unit oil question
I believe most all gear oil would have anti-foaming "agent"s in them or they would blow foam out the breather when used in most any gear box.
I would be more inclined to believe there may be some anti-corrosive, or dispersant's involved though.
I've used regular 80-90 without issue, and actually preferred it in one unit that had water intrusion issues which negated change out often. I found that the non-marine version was less likely to keep water in suspension, letting it settle out, and then drain out easily.
