The reason for this is that the threaded section of valve stems tend to be either brass or stainless, neither of which are very compatible with aluminium.
Use of an anti seizing compound is highly recommended
"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"
I've fitted some hp shiney steel truck ones to all our cars with no bother.
I managed to acquire some truck ones after a truck had new tyres in the yard and the fitter forgot the bag of caps, used them on the ZR, 2 rusted on, 2 got stolen.
Home to black Alfa Romeo 159 3.2 V6 Q4 ,green MGF VVC andred MG Maestro T16.