Yamaha Lower Unit Assembly - 6G9-45300-03-EK. OEM Yamaha Gearcase Replacement for Reliable Propulsion. The Yamaha Lower Unit Assembly - 6G9-45300-03-EK is a genuine factory-built gearcase designed to restore smooth, efficient power transfer on your Yamaha outboard. As a complete OEM assembly, it arrives with key components-including the gear housing, driveshaft, propeller shaft, bearings, seals, and shift shaft-pre-installed and factory-tested. This ensures a precise fit, easy installation, and