I have also found that all service parts should be replaced every time the tire is dismounted. My 2006 XL-7 uses a Schrader model. Information for what make and model your system uses try
The Tire Rack - Your performance experts for tires and wheels and find the link to the TPMS. The service kits are also listed there. The service kits consist of a rubber grommet, an aluminum retaining nut, a special nickel- plated valve core and an O.E. valve cap.