Boats with motor problems???
If I may add a bit here. On an older vessel you have to consider if parts are available as well as the condition. Mine for instance (50 hp Pathfinder - VW) which has 7000 hours and was maintenenced well over the past 22 years. It looks and runs well. The problem I may get into is when I need parts. They are rare. I keep in contact with the manufacture and there is some stuff that''s not available anymore. Fortunately, I''m a Machinist/ Toolmaker.
Contact the manufacture of the engine in question and ask them how many hours one could expect to get fro their engine. Then look at the condition of the motor. If it''s all dirty and rusty, chances are that it didn''t get much attention. Bad motors are one reason some sell their perfectly good looking vessel. Some vessels, the motors are almost impossible to get out. Another reason to sell!