This O-ring seals the connection between the power take-off unit and the engine on the host tractor. It sits in the groove at the PTO housing interface, preventing oil leakage from the transmission or engine sump along the rotating shaft. A degraded or flattened O-ring allows fluid to weep past the joint, which can lead to low oil levels and eventual bearing damage. The part is manufactured by AGCO to match the original cross-section and durometer, so it seats correctly in the housing groove without requiring additional sealant. On reinstall, ensure the groove is clean and dry before fitting the ring.