In case anyone else has a Boxster that is exposed to road salt in the winter (the previous owner of my car drove it year-round in Chicago), I've found an easy way to rejuvenate your colored crest wheel center caps.
My crests were VERY faded and had lots of little scratches. I bought some clear fingernail polish, and gave each crest a single coat. The red, yellow, and black INSTANTLY showed their deep, full colors again. I applied another 3-4 coats to protect the crests in the future (after seeing how much a NEW set of colored center caps cost.
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Sorry I didn't get any "before and after" pics. I was too excited to grab a camera when I saw how the first center cap turned out.
Just thought I'd pass this along.