This O-ring seals the gearbox housing at the shaft passage, preventing lubricant leakage and keeping contaminants out of the gear train. It sits in a machined groove on the gearbox cover or input shaft flange, where it compresses between two rigid faces to create a static seal. A degraded or flattened O-ring allows oil to weep past the seal face, leading to low fluid level and eventual gear or bearing damage. As an original AGCO component, the cross-section and durometer match the groove geometry of the housing, so the seal compresses to the correct interference without over-stressing the groove walls. On installation, ensure the sealing surfaces are clean and dry; apply a light coat of gearbox oil to the O-ring before seating it.