When my car was only 4 model years old with less than 55,000 miles on it, I took it in for regular maintenance and was told that the lug nuts were all swollen and would have to be replaced. At $7.50 each, the parts alone cost $150. I was told that I would have to replace them sooner or later, even if it wasn't that day, or else I'd never be able to rotate the tires or replace a flat tire ever again. The master mechanic told me that this has been an ongoing problem that Ford has refused to deal with--and that they're putting the aesthetics of having aluminum caps on the lug nuts to match the wheels over the structural integrity of all-steel lug nuts.