Yamaha Lower Unit Assembly - 6N0-45300-20-4DYamaha Lower Unit Assembly Gearcase Component 6N0 45300 20 4D Overview On any outboard, the lower unit is where the real work happens once power leaves the engine. Ive seen boats lose smoothness and efficiency just from wear down there, even when everything else checked out fine. When you install a solid assembly like this, you feel it right awayclean engagement, quieter operation, and better push through the water. Its the kind of upgrade that brings