[Fitz]

Chesapeake:

Your mechanic's primary findings generally indicate a solid engine: "runs well, holes and pistons are clean, compression even". The only negative findings you indicate are "cooling water leaks" and "exhaust leaks". Please give us more information about those problems. They could indicate anything from trivial annoyances to a cracks in the block.

Assuming you haven't found any major problems, I'd highly recommend that you replace your ignition wires before making your decision. Their condition can make a huge difference in performance, and they're relatively cheap and easy to replace.

My general recommendation would be stick with the engine you know rather than gamble on someone else's used engine, unless you're really forced to do so. The price of the Yamaha seems to me be too low to indicate a decent engine, and the fact that the dealer passed on it even at that price gives me additional cause for concern.

Whatever you decide, good luck.