Mercury - Seawater Pump Seal MerCruiser Bravo Cooling System Marine Polymer Seal 8M0146317. Overview. When you spend your weekends running a big MerCruiser inshore and offshore, you get pretty tuned in to the little sounds and rhythms of the engine. You know when everything feels steady and effortless, and you know when something is just a touch off. A reliable seawater pump seal might not be the flashiest part on your boat, but it is one of those behind-the-scenes pieces that keeps everything r