It was amazingly difficult to find these 4″ rubber disks. They’re simple and their purpose is to seal the bronze end caps of the engine heat exchanger to the long tube part of the exchanger. Each time we clean out the heat exchanger, we’re supposed to replace the gaskets. Yet, we couldn’t find new ones so we kept re-using the old ones (on the right). In prep for our upcoming Sacramento Delta cruising, we just serviced the engine’s fresh and sea water systems. Clean as a whistle they are now! When I approached the local chandler, I even showed them the ones available online through Fisheries Supply but the local chandler had never heard of such a thing. Their engine repair guys didn’t know what these were either. Huh??? how could that be??? So, forgetting about buying “local” I bought these 4″ ones via Fisheries Supply and made sure to buy an extra pair plus an extra bronze end cap for our spare parts bag.