You may not have had them much,but they are getting more and more common.
FWIW,buy the kit that has the torque wrench,valve stem core tool and the service kits.
Bridgeport/Schrader has a complete kit our shop uses.
It is recommended to replace the O-ring,nut,and crush sleeve on most TPMS sensors when servicing tires.
The GM valve stems are available from them and as well from the dealer.

I attended the training seminars and the proper way to dismount a tire wiht a TPMS sensor is remove the valve core,then nut and push the sensor inside the tire and break the tire down.
Of course the guys in the shop skip that and break the bead 180 degrees away from the sensor.

The problem our shop exprienced is Northern climates with salt on the roads can sieze up the valve cores.We have snapped many a sensor that is corroded from winter driving.
It is important to have correct valve stem caps on the sensors.
Fancy chrome caps,or regular plastic ones do not keep moisture out.
Make sure you "test" the valve core before going further.If it is not going to come out,tell the customer heads up that a new sensor may be required.Make sure you get price and availability before proceeding so you wont have a sitting duck on your hands.
Hope this helps.