So now that dirt track season is over and I'm moving on to newer and cleaner things, I'd like to shine up my Sigma 70-200. I'll try to find another camera to post a photo of what it looks like attached to my 40d. The 40d is new and sleek, but the 70-200 lens seems somewhat porous in material, and dirt has clung to it. (i've used the 70-200 on the track for a season, and the 40d for only a couple races). When I try to rub it off with my sleeve, it doesn't really come off, it feels like i'm rubbing dirt into a sponge. Any ideas on how to get this puppy clean?