The Coke is acidic, but modern Coke isn't as aggressive as it was when our grandfathers were shining their military uniform buttons with it. I'd probably go straight to Naval Jelly ®
or something similar (see Naval Jelly
for a non-commercial description), which is also acidic, but so far I have only polished chrome stuff with rust pitting, not tried this chemical attack.
The wax - or some other clear sealant
- is important because much of the visible rust is often from some tiny holes in the chrome plating, but spread out over the surface. Polishing removes rust deposits from the surface of the remaining chrome, but leaves the rust spot. Sealing the surface can help prevent further rusting.
Another option is re-plating
, if you can find a bumper shop that still does it, but I would guess that new caps might be cheaper. I'd try polishing and seal like the other guys said, first.