This O-ring seals a connection point within the hydraulic system of the parent harvesting machine. It sits between two mating surfaces, preventing fluid leakage under operating pressure. A degraded or nicked O-ring allows external seepage and can introduce air into the circuit, causing spongy actuator response. The manufacturer machines this seal to the same cross-section and durometer as the original assembly, ensuring it compresses fully into the gland without extrusion. Replace the O-ring whenever the joint is opened; lubricate it with clean hydraulic fluid before installation to prevent rolling or pinching.