Yamaha Lower Unit Assembly 99999-03364-00. Overview. The Yamaha Lower Unit Assembly 99999-03364-00 is a genuine original equipment manufacturer component designed to deliver efficient power transfer from the engine to the propeller. This assembly plays a critical role in your outboard's drivetrain, ensuring smooth operation, responsive handling, and reliable performance on the water.. Built to handle demanding marine conditions, the lower unit assembly supports consistent propulsion while protec