One of my friends has used generic oil in his boat for the last several seasons because after spending the money on the boat as well as getting it launched, there wasn’t much cash left for oil. At the end of last season, his motor was starting to sound odd so he took it in to be prepared. It turned out that the motor was pretty gummed up from the generic oil.
He ended up having the motor de-carbed and started to use Yamaha 2M oil. This year he is finally going to get a chance to run his engine with the new oil that he is trying. He is hopeful that the oil will work a lot better, since in the long run, he spent more on the repairs than he did on the oil.