This fuel injection O-ring seals the connection between the injector and the fuel line, preventing fuel leakage and maintaining system pressure. It sits at the interface where the high-pressure fuel line meets the injector body, a point subject to thermal cycling and vibration. A degraded O-ring causes air ingestion or fuel seepage, leading to hard starting, rough idle, or a drop in engine power. This original AGCO part is molded to the same cross-section and durometer as the original seal, so it seats fully in the groove without requiring additional sealing compounds. Replace the O-ring whenever the injector is removed or the fuel line is disconnected.