Mercury - Quicksilver Gear Housing Gasket Lower Unit Seal Marine Composite 430331. Overview. A good seal means a healthy drive. The Mercury Marine 430331 Quicksilver Gear Housing Gasket keeps water out and gear oil in, ensuring your lower unit stays properly lubricated and protected. Built to factory specs, this gasket fits a wide range of Mercury, Mariner, and MerCruiser drives, including Alpha One Gen II sterndrives and 40-300HP outboards. Made from durable, marine-grade material, it's designe