This O-ring seals the clutch assembly, preventing hydraulic fluid or oil from leaking past the piston or shaft interface. It sits in the groove machined into the clutch housing or piston, maintaining pressure integrity during engagement and disengagement. A degraded or hardened O-ring allows fluid bypass, which causes clutch slip, delayed engagement, or loss of drive pressure. The original profile matches the groove dimensions so the seal compresses to the correct cross-section without extrusion. On reinstallation, ensure the sealing surfaces are clean and free of burrs, and lubricate the O-ring with assembly fluid to prevent rolling during fitment.