I had same problem.
Washed, polished, but still faded and dull black, but didn't want to paint them.
I tried "Black Again", that I use on plastic and rubber parts. Actually read what it said on the bottle, good on metal too! I used a sponge applicator. The wheels now look new!
Bought the stuff off the internet a few years ago, still good.
(I have no connection with the product).
