[CRH911S]

89911 needs to remove the tire from the wheel so that a competent tire person can inspect the inside of the tire. Herein lies the history of the tire and subsequent care that it recieved by the owner. For instance, possible damage due to neglect of an earlier repair and possible destruction of the inner liner, as well as a history of over or under inflation. The valve stem is suspect here and I think a couple of things should be considered such as proper installation and possible material defect.
As far as rubber vs metal valve stems it's unlikely the heat or the speed have any adverse affect on the rubber stem. Under normal street driving of course. If steel turns your crank and this is what makes you feel safer then go for it but it's not really necessary for the duty our cars see.