Yamaha - Lower Unit Assembly Lower Unit Drivetrain 6DX-45300-12-8D. Overview. When a lower unit starts making noise or loses confidence in the water, it's usually time to stop guessing and replace it. I've seen guys try to piece together repairs, but once internal wear sets in, it rarely holds up long-term. A complete assembly like this gets everything back in line-gears, seals, and shafts all working together like they should. Bolt it on, and you're back to smooth, dependable performance.. Key Features. Complete Lower Unit Assembly - Includes major drivetrain components for a full replacement solution.. Smooth Power Transfer - Restores consistent performance from the engine to the propeller.. Sealed Gearcase Design - Helps protect internal components from water intrusion and contamination.. OEM Precision Fitment - Matches original specifications for proper alignment and installation.. Engine & Boat Compatibility. Designed for Yamaha outboard engines with compatible lower unit configur