WE lost four tires in 08 Possibly on our F150...because the Chinese valve stems did not have any UV protection compounds in the rubber. Distributor replaced all the tires, and stems of course.
I have seen cracked rubber stems on cars but it has been a long time.The "high Pressure" brass tube with rubber cover stems can be a problem too. At a Truck stop in Ky someone stepped on and bend them and they leaked badly.
Replaced them with short stainless bolt in stems. Look good on the aluminum wheels too. Whoever owns our former Wheel now may still have those in the wheels.
Also buy stainless caps if they don't come with the stems with rubber gaskets inside. Do not use the cheap plastic caps.
On our Mh Left front tire was low. The valve was loose and without that metal cap with seal inside the tire might have went flat.
Bought a Snap On tire stem tool $10.00, from a Truck, that happened to be near by, and checked and tightened all of them. This was in Shawnee Oklahoma. Rally at the Convention Center