[jakeru]

'Those cool valve stem covers' isn't very clear to me what you're talking about. If you are talking about aftermarket aluminum valve stem covers on brass valve stem threads, then yeah, I could easily see those corroding when exposed to wet weather/elements.

The "tecquipment" colored-crest valve stem covers I have are actually made of plastic. They have very thin, electroplated metal on the outer visible surfaces. Nice and lightweight that way, and probably won't corrode on brass valve stems like, say, aluminum valve stem caps would. I'm actually not crazy about how they look, but I'm not sure I've found anything that's better, except for maybe just plain black plastic valve stem caps (for a lower-bling factor option.)

Brass valve stem caps wouldn't corrode to the brass valve stem thread, but are way heavier than either aluminum or plastic.