This O-ring seals hydraulic connections on the engine of the host tractor. It sits between mating flanges or ports to prevent fluid leakage from pressurized lines. A degraded O-ring causes external oil seepage and a gradual loss of system pressure, which can lead to cavitation in the pump. The manufacturer machines this seal to the same cross-section and durometer as the original, so it seats fully in the groove without being over-compressed. Replace the O-ring whenever the joint is opened; lubricate it lightly with clean hydraulic fluid before installation to prevent rolling or pinching.