Lower Unit Assembly - 6P3-45300-51-8DYamaha Lower Unit Assembly Gearcase Component 6P3 45300 51 8D Overview When a lower unit starts going bad, you usually feel it before you see itnoise, vibration, or just not running as smooth as it used to. Ive swapped enough of these to know that going with a complete assembly saves a lot of guesswork and time. Everything is already matched and set up the way Yamaha intended. Its the kind of replacement that gets you back on the water with confidence