Hmmm I've hade aluminum caps on nearly every car in the last 25 years and never had an issue (currently on 10 vehicles in the garage.....and the bicycles )Also DO NOT put aluminum valve stem caps on your valve stems. They seize onto the brass. !
Application of a little anti seize should resolve the problem entirely. If you occasionally take off your valve caps to check the tire pressure, it really shouldn't be a problem.I'm sure some of it is definitely climate dependant too. I live in the high desert where nothing rusts.
Wondering if you can simply lube the stem to avoid the issue and still use whatever caps you want.
http://tires.about.com/od/Tire_Safety_Maintenance/a/Achey-Breakey-Parts-Tpms-And-Corrosion.htmProblem: Metal Valve Caps.
While the bright and shiny chromeplated or metal valve caps that you see everywhere are often a nice effect compared to dull black plastic caps, when it comes to TPMS stems, they're a clear and present danger. Metal caps can easily cause corrosion on the threads of TPMS stems as well as beginnning to corrode themselves. The result is all too often that the cap will rust-weld itself to the stem, leading to outcomes from the cap simply seizing when a technician tries to remove it, to crossthreading issues, or even having the stem break off entirely. When the valve stem is a nonremovable part of the TPMS monitor, this goes from being a minor issue to a critical and often expensive problem.