This O-ring seals the interface between the feed pump and its mounting face on the tractor's hydraulic system. It prevents external leakage of pressurized fluid at the pump outlet, maintaining system pressure for downstream functions. A degraded or hardened O-ring causes fluid seepage at the pump flange, leading to pressure loss and aeration of the hydraulic circuit. This component is manufactured to the original cross-section and durometer specification, ensuring it seats correctly in the gland without extrusion or rolling during installation. Replace the O-ring whenever the pump is removed for service; lubricate the seal before assembly to prevent pinching.