Mercury - Water Pump Gasket Cooling System Service Marine Composite Seal 8M0090319. Overview. If you've been on the water long enough, you know that an engine's cooling system is one of those quiet, dependable lifelines you rarely think about-until something goes wrong. A steady stream from the telltale, a smooth idle after a long run, that comforting sense that your motor is staying cool even when the day gets hot… that's the kind of peace a well-sealed water pump delivers. The Mercury 8M009031