Yamaha - Lower Unit Assembly Complete Drivetrain Assembly 6FR-45300-03-NA. Overview. The Yamaha Lower Unit Assembly 6FR-45300-03-NA is what takes all that power from your engine and actually puts it into the water where it counts. When a lower unit starts going bad, you'll feel it right away-noise, vibration, or loss of push at the prop. Instead of chasing internal damage piece by piece, replacing the full unit is usually the cleanest and most reliable move. It gives you a fresh setup below the waterline so you can run hard without worrying about what's going on down there.. Key Features. • Complete Drivetrain Assembly - Replaces internal gears and components in one unit for dependable operation.. • OEM Fit Precision - Built to Yamaha specifications for proper alignment and straightforward installation.. • Smooth Power Transfer - Supports efficient thrust and consistent performance under load.. • Corrosion-Resistant Construction - Designed to handle harsh marine environments and long-t