Yamaha Lower Unit Assembly - 6G5-45300-21-EK. OEM Yamaha Gearcase Replacement for Reliable Power and Performance. The Yamaha Lower Unit Assembly - 6G5-45300-21-EK is a genuine factory-assembled lower unit designed to restore smooth propulsion, durability, and factory-spec efficiency to your Yamaha outboard. This complete unit arrives pre-assembled with critical internal components-including driveshaft, shift shaft, gears, bearings, and seals-ensuring a precise fit and optimal performance right o