Like Dennis, I also believe that the 2QM15 was the earlier engine. Yanmar redesigned that engine and then renamed it the 2GM15. The GM engine was designed to reduce the vibration that's typical of the QM. I have the QM in Mondial (hull number 215). Overall, they are durable little engines. I really wouldn't worry about the mere fact that it's a raw water cooled engine. On the Chesapeake, we run in brackish water and most of them are still chugging along. You could pull the zincs (there's one in the block and another in the head) to verify that they are in good condition. Then, I'd have the surveyor look at it. If you're still concerned you could have a separate engine survey done by a mechanic.
