16818-ZY3-003 O-Ring - Overview. The 16818-ZY3-003 O-Ring is a precision-engineered sealing component specifically designed for Honda marine engine fuel systems. Its primary role is to provide a reliable seal within the water separator fuel system assembly, preventing leaks of oil, fuel, or other fluids. This essential part supports the fuel system in maintaining optimal performance and reliability. Crafted to exact factory specifications, it ensures seamless integration with existing parts, mai