Mine looks the same after a season of driving. So while stored for the winter I take a small round brass brush in my dremel tool & clean up the contacts & rotor tip nice & shiny clean. Then wash them out with brake cleaner & compressed air.
So far 20,000 + miles & working fine. The corrosion/eroding on the cap does not appear to get any worse from year to year, so far!
Maybe I'm just a cheapscape,
but it's working for me.
Craig