Yanmar 12 Seafarer 30
Had a 2GM in an S2 I owned. Great little motor. I took a couple of classes on the engine through Union City Tech and Mack Boring (Largest East coast dealer w/Yanmar.)
Instructor says Yanmar realisticlly is a 10,000 hour engine. And it is a simple one to work on. Of course depending on it''s location in your boat.