Yamaha - Lower Unit Assembly Outboard Drivetrain 6L2-45300-13-4D. Overview. When a 25 horsepower Yamaha starts feeling off, the lower unit is usually where the problem shows up first. You'll hear it in the shift or feel it in the way the boat runs. This is the kind of replacement that brings everything back to smooth, predictable performance. It bolts up clean, runs quiet, and gives you that solid feel you want when you're out working or just enjoying the water.. Key Features. Smooth Power Transfer - Delivers steady engine output to the propeller with minimal vibration.. Corrosion-Resistant Housing - Built to handle saltwater and tough marine environments.. Factory-Spec Fitment - Designed for proper alignment and seamless installation on Yamaha outboards.. Durable Internal Gearing - Supports long-term reliability under regular use and load.. Complete Assembly Unit - Pre-assembled design reduces downtime and simplifies replacement.. Engine & Boat Compatibility. Designed for Yamaha 25 ho