Capt. John. I had a 1988 Volvo that used a 350hp GM engine. Pluses..water impeller on engine block, didn't have to tear down lower unit to exchange. I always carried a spare.. one time replaced at sea...10 min job. Lower unit was sweet, didn't have to remove every season... I had it 15 years, never had it off. Lower unit uses 10-30 oil, Had to change hydraulic trim hoses and prop seals. That was it. Minuses....finding Good Volvo shop.
John if you look at 4-stroke O/B, check out Honda.... third season so far.... love it... Quieter than the rest.... they must be bullet proof. Check the boat/motor sections of some of the sites like Walleye central.....very few reports, in a search all the others have multiple hits. I think it is just because they have very few breakdowns.
Good luck