Goodyear dealer couldn't put metal valve stems on the wheels... but they did put on a heavy duty rubber/metal valve stem.
Tires look awesome, touch taller, touch wider.
To the claim of never seeing a bad valve stem, owner of the dealership looked at the valve stem, and said "You're lucky, these were not going to last much longer".
TST claims you don't need metal valve stems with their non flow through TPMS. Did they cause cracking, I don't know, but they were worse on one side of the trailer than on the other side. West side of the parked trailer was worse, East side was also shadowed by another TT.
I hated spending the money, but also recognize that we use the TT for long trips. We don't take weekend trips in it. A trip interruption with damage could be quite an issue and easily worth a $600 insurance policy :)