This gearbox o-ring seals the interface between the gearbox housing and its cover or shaft, preventing lubricant leakage and keeping contaminants out of the gear train. It sits in a machined groove on the mating face; compression of the o-ring creates a static seal that holds transmission oil under normal operating pressures and temperatures. A hardened or flattened o-ring will allow oil to weep past the seal, leading to low lubricant level and eventual gear or bearing damage. As an original AGCO part, the o-ring is molded to the specified cross-section and durometer so it fills the groove correctly without over-compression or extrusion. On reinstallation, clean the groove thoroughly and inspect the mating surface for burrs before fitting the new o-ring.