Yamaha - Lower Unit Assembly Gearcase Component 6P2-45300-21-8D. Overview. On these F250 setups, the lower unit is where everything comes together-power, control, and reliability. I've seen boats lose performance not because of the engine, but because the gearcase wasn't transferring power cleanly anymore. When you bolt on a fresh assembly like this, the difference is immediate-quieter operation, smoother engagement, and better push through the water. It's one of those upgrades that brings the whole motor back to life.. Key Features. • Complete Gearcase Assembly - Provides a full replacement with matched internal components.• Efficient Power Transfer - Delivers consistent output from engine to propeller.• OEM Precision Fit - Designed to Yamaha specifications for proper alignment and installation.• Corrosion-Resistant Build - Handles harsh freshwater and saltwater environments with durability.. Engine & Boat Compatibility. Designed for Yamaha F series outboard engines, including high-ho