Let me guess, vented cap???
Seal the vent up, it's not needed. A little silicone grease on the bottom lip wouldn't hurt either. Someone over at Ford decided a long time ago that the distributor cap needed a vent for the ionized air or condensation (basically a fix for a non-existent problem), GM and Chrysler evidently felt it wasn't needed as I've only seen them on Fords and some aftermarket stuff. Putting the distributor on the front of the engine wasn't a very good idea either.
Cadmium plating on the iron parts buys you about a month of rust prevention (or one heat cycle, whichever comes first). Basically, it's just to keep the part from rusting till you buy it.
Black oxide is the "eco-friendly" replacement for cadmium plating (which means there's a 50/50 chance the part's already rusted out of the package).