New SEI (Sterndrive Engineering) 4-Cylinder Replacement Mercury & Mariner Outboard Gearcases

Discover our range of New SEI Gearcases designed for Mercury & Mariner 4‑cylinder outboards. These high-quality lower unit replacements offer direct compatibility with a wide range of engine types. Each gearcase is a ready-to-install assembly, including the water pump, and is engineered for ease of replacement and backed by SEI’s commitment to performance and durability. Whether you're performing maintenance or upgrading your drive, these new SEI units offer exceptional value and peace of mind with the fault-free three-year warranty.