This O-ring seals the wet clutch housing, preventing pressurized oil from leaking past the piston or clutch pack. It sits in the groove between the stationary housing and the rotating drum, where it maintains a fluid-tight barrier under operating pressure. A worn or hardened O-ring allows oil bypass, which reduces clutch engagement pressure and causes slipping or delayed engagement. The original AGCO O-ring is molded to the correct cross-section and durometer for the groove geometry, so it seats without twisting and resists extrusion under load. On reinstall, clean the groove thoroughly and lubricate the O-ring with clean transmission fluid before assembly.