New engines can fail too!......Whether fresh or seawater cooled, the thing most likely to fail is not corrosion, but the rubber impeller. A good friend who lived aboard for 15 years told me to inspect the impeller once a year, and if it looks brand new, throw it away and put in one that IS brand new! When I bought Ragtime, my Perkins 4108 diesel
overheated a little. The heat exchanger was nearly clogged with bits of rubber broken off "almost"good impellers! If properly maintained, a diesel will outlast a fiberglass hull, and they will last forever!