Unless you are very experienced with marine diesel engines I would recommend having a certified Yanmar (works primarily on Yanmars) mechanic inspect the engine. They can generally tell just from starting and running an engine what shape it is in. I would also highly recommend making an oil analysis part of the engine survey, that will tell you what the inside of the engine is like. 3000 hours, if the engine has had scheduled maintenance, is nothing to worry about. Many engines will go 6-8000, or more, before rebuild.
SV Laurie Anne
1988 Brewer 40 Pilothouse