Hardcore heat cycles or repetitive removal can over time wear on the O-rings in the AOS. Maybe you like the peace of mind or have a show car you always want in perfect condition, this rebuild kit will get you all sealed up! It comes with all necessary o-rings for a full replacement. (6) O-rings included: (1) Large for the bottom of the body, (1) for the inner seal of the core to the body, (1) for the top core to body seal, and (3) fitting seals.