If you are not the original owner you could have an aftermarket system. You can tell if that is the case by looking at the valve stems or just asking Discount Tire to show you what they are rebuilding. I wouldn't jump to the conclusion they are trying to rip you off yet. If they are not there it could just be a mistake, humans do make mistakes.

A rebuild kit replaces the parts in the valve stem that degrade and can cause a leak. It would be SOP for any tire store to replace these parts just as they replace a normal valve stem when you replace a tire.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas