Firstly, the surveyor did a great job elsewhere.
The seller is a decent guy, I am cross with him for misleading me, but I don't think he did it on purpose.
Hmmm. You are a very
nice guy--maybe too nice. To me this feels like a "looks like a duck, quacks like a duck, is a duck" situation.
I bought a boat with a known 20yr old 2GM20F and the surveyor stated that he wasn't doing an engine analysis or anything, wasn't a diesel expert, etc. but he observed the engine while running, looked at the exhaust, checked the real RPM against the tach, checked max RPM, checked general condition of hoses, looked at the primary fuel filter water catcher, and spotted a pretty good (and obvious) fuel leak. I think an engine leaving a black streak below should have been noticed. Seems like the oil-slick bilge should have been noticed.
As for your other duck, maybe he really is that clueless--more pleasant to think that than to believe he lied. But the "new" engine? 100 hours, but with a cut wire to the hour meter? I'm hearing quacks.
Maybe you won't be getting anything back from them, but I don't know that I'd be recommending that surveyor or having a beer with that seller.