Is there a way to polish plastics like you polish metals? Like fan shrouds and fuel tank covers? A list of materials used and process (if any different than polishing metal) would be great.
I had deep scratches on the lower black section on my rear bumper that I was able to repair using a high speed cotton wheel and some polishing compound. You should be able to remove oxidation, light scratches using this method.
I have had good luck with Meguiars products too. If not, paint them. SEM makes a good trim black that works good on plastic, I have had great luck with it. You can find it at most auto paint supply stores.