Yamaha - Lower Unit Assembly F25/T25 Complete Drivetrain Assembly 6FM-45300-10-8D. Overview. The Yamaha Lower Unit Assembly F25/T25 6FM-45300-10-8D is what actually puts your engine's power into the water, and when one starts going bad, you feel it right away. Noise, vibration, or slipping under load are usually the first signs something's off down there. Instead of chasing worn gears or internal damage piece by piece, swapping the full unit is usually the cleanest fix. It gives you a solid, ready-to-run setup so you can get back on the water without second-guessing it.. Key Features. • Complete Drivetrain Assembly - Replaces internal gears and components in one unit for dependable performance.. • OEM Fit Precision - Built to Yamaha specifications for proper alignment and straightforward installation.. • Smooth Power Transfer - Supports efficient thrust and consistent operation across all speeds.. • Corrosion-Resistant Construction - Designed to handle harsh marine environments and lon