I was cleaning my car recently and was disappointed to see that the wheel centre caps had started to "corrode" - I'd only bought them about 6 months ago. I ordered a new set from ebay and when I was changing them over I noticed that there was a protective clear film on them, which I had omitted to remove originally - silly me! I think that the clear film was retaining some water and causing premature corrosion. Anyway, new ones now fitted (with protective film removed).
New ones fitted
New ones fitted