It is a common problem on the alloy pullies, i have piper ones on mine and there is certainly some wear on them,

We offer these,

http://www.shop.motorsport-developme...leys-863-p.asp

Which are hard anodised, which from what i have seen stops this from happening. I think i will be fitting some to mine.

The quaife ones are also very good, and they offer a steel version.