Yamaha - Lower Unit Assembly Gearcase Component 6FJ-45300-03-8D. Overview. The Yamaha Lower Unit Assembly 6FJ-45300-03-8D is what keeps your power actually making it to the water. When a lower unit starts going bad, you'll feel it-noise, vibration, or just not getting the push you're used to. This assembly handles everything from gear transfer to prop rotation, so it has to be solid. If you're replacing a damaged unit or dealing with gear issues, this is one of those upgrades that brings the motor right back to life.. Key Features. • Efficient Power Transfer - Delivers engine power to the propeller for smooth and reliable performance.. • OEM Fit Precision - Built to Yamaha specifications for proper alignment and straightforward installation.. • Pre-Assembled Gearcase - Includes internal components for a complete replacement solution.. • Corrosion-Resistant Construction - Designed to withstand saltwater, freshwater, and harsh marine use.. Engine & Boat Compatibility. • F200 2004-2017• F