From my perspective as a Mercury, Evinrude and Yamaha dealer, this advice is about as good as it gets. I would add: If it's an Optimax, I would check to see if the compressor has been replaced-they usually go after 300 hours or so. If budget allows, have the technician check the o-rings at the top of the cylinder block. Water intrusion through heat deteriorated o-rings is a major cause of failure in those powerheads. Evinrude, I would get temp readings for the on-board EMM (Evinrude for computer). Overheats of the EMM cause problems and failure. Early Yamaha HPDIs can have fuel lean-out issues which can cause powerhead failure. As stated if it's a computer controlled newer engine, downloads will reveal engine fault history and current existing faults. Beware of any "rebuilt" powerheads; "remanufactured" or "remans" can be acceptable. Good luck but go in with your eyes open.