When you purchase an older used boat, it may have an engine that is no longer in production, and parts may be hard to find. With the cost of new diesels starting at around $7,000 for a miniscule 9 hp Yanmar, fixing the old engine is probably a very economical idea.
Unfortunately, most service department mechanics are good at repairing engines that are less than ten years old and while the new factory parts are still available. But, with most boat engines, ten years may just be the break in period. It is in the 15 to 20 year age range that they begin to fail and need parts.
I am often asked questions like, Where do I get parts for my Albin engine?, or, Who builds Palmer engines?, and ?Do they still make Passagemaker engines??.
One proposed way to solve the older engine problem is to buy an identical second engine. Find another old, and hopefully worn out, boat for sale, which has an operating engine just like yours. Buy the old wreck with the good engine for three of four thousand. Steal the engine and put it in the back of the garage for spare parts, and then sell that older boat without an engine, for two to three thousand. It is actually easy to sell older engineless sailboats, especially if they have a secondary outboard motor mount. It is a little more difficult with a power boat, to sell it without an engine.