Mercury - Gear Case Seal Kit Outboard Lower Unit Marine Polymer Seal 8M0082880. Overview. If you've spent any time around small outboards, you know how much peace of mind comes from a lower unit that stays sealed tight. It's one of those simple things you don't think about often - until a worn washer lets water sneak in or gear lube drip out. The Mercury 8M0082880 Gear Case Seal Kit is the kind of quiet, dependable part that keeps your motor protected trip after trip. Whether you're running a li