Recently bought a 1983 Hunter 34. Awesome boat. Sail here in Holland MI, went out for the first time last Saturday, It was freezing. The Yanmar Diesel ran fine but it does have the most hours i have ever seen on any engine. It has 1,380 hours. The surveyor said that these engines are pretty bullet proof. At what point is it time to have it rebuilt? It smokes a lot at high RPM's but otherwise starts right up and runs fine. The previous owner was meticulous about the boat so i am confident it was maintained. Any suggestions or advice or maintenance tips about this engine would be great. It is the 20 horse model.