This O-ring seals the hydraulic pump housing, preventing fluid bypass between the pump's internal pressure zones. It sits in the groove between the pump body and the cover plate, where it maintains a static seal under operating pressure. A degraded or compressed O-ring allows internal leakage, which reduces pump output volume and can cause cavitation noise. As an original AGCO component, the cross-section matches the groove depth of the original housing, ensuring the seal compresses to the correct height without over-squeezing. On reinstallation, clean the groove and lubricate the O-ring with clean hydraulic fluid before seating.