Mercury Oring - 25-8M0137333. The Mercury Oring - 25-8M0137333 is a genuine OEM replacement part designed to maintain a watertight seal in Mercury marine engine assemblies. Built for precision and durability, this O-ring is engineered to meet exact factory specifications, ensuring proper fitment and long-lasting protection against leaks and pressure loss in critical systems.. Key Features. Authentic Mercury Replacement Part - Manufactured to OEM standards for optimal reliability. Tight, Leak-Res