I have these wheels on my car that are in decent shape. Problem is that they have these center caps on them that have rusted overtime. I tried to get them off to clean them, but have had no luck. They seem to turn around freely on the wheel though. I decided to just try and go at them with aluminum foil while they are still on the wheel. Except, I need to take them off to scrub them harder and get into some other places that I can't reach. Any ideas on how to get them off?