The O-ring prevents oil from leaking out of the engine casing along the bore for the kickstart shaft. This rubber seal should be replaced during an engine overhaul. Install the new O-ring with a bit of grease. The seal fits Vespa 50, PK 50-125 S-XL2, PX, Cosa, Sprint, and many more scooters.
End-Year-Sale up to 50%
