- Those engines, if properly maintained per the manual could last 8 - 10k hours. Ask the owner for the receipts for all the services, down load the service manual from Yanmar and check that the services covered ALL the elements that specified to be done. Things that usually are not done on the scheduled time by DIY
servicers are the replacement of all rubber hoses, the valve back lash adjustments, exhaust
elbows etc. If you look in the service tables you will note often the comments is "At x number of hours OR by x number of months or years which ever comes first." You say it has been professionally serviced, so all these items should have been done and signed off by a professional mechanic
over the life of the engine and hopefully the service manual has been filled in too. Applies to sail drives too.