I have a Yanmar 3 3GMD engine that is close to 30 years old. The engine runs and fits the boat well. Being direct sea water cooled I could see in the future it may give me problems. Could the engine be rebuilt with a new block and other required parts economically and be good for another 20 or so years? I have heard these old engines are built heavy than the newer Yanmars. I like the fact it is direct sea water cooled as it is very simple and has fewer parts to break or maintain than a freshwater cooled engine. Seeing the engine has lasted 30 years so far seems to indicate direct sea water cooled was not so bad.