Yamaha Oil Filler Plug YF1-58523-31-40. Overview. The Yamaha YF1-58523-31-40 Oil Filler Plug is a genuine original equipment manufacturer component designed to securely seal the engine oil fill opening and protect the lubrication system from contaminants. This plug helps prevent dirt, debris, and moisture from entering the engine while maintaining proper oil containment during operation.. A properly sealed oil system is essential for maintaining engine lubrication and long term reliability. Over