Yamaha - Lower Unit Assembly Gearcase Component 6P2-45300-41-8D. Overview. On an F250, the lower unit takes all that power and turns it into forward motion, so when it's off, you feel it right away. I've worked on setups where everything up top checked out, but the gearcase was the weak link causing noise or poor performance. Swapping in a complete assembly like this brings everything back to smooth, predictable operation. It's the kind of fix that makes the motor feel solid again the moment you hit the throttle.. Key Features. • Complete Gearcase Assembly - Provides a full replacement with properly matched internal components.• Smooth Power Transfer - Delivers consistent output from engine to propeller under load.• OEM Precision Fit - Built to Yamaha specifications for correct alignment and operation.• Corrosion-Resistant Construction - Designed to handle harsh freshwater and saltwater environments.. Engine & Boat Compatibility. Designed for Yamaha F series outboard engines, including