I'll second the recommendation for NevrDull. Bought a can at my local Ace Hardware. Inside is a rolled-up soft rag that smells like petroleum; you tear off a small piece and use it to clean up the exhaust. It worked pretty darn well for me. The next time I went to clean them all I used was a paper towel and the residue seemed to come right off so I don't think that you have to use it everytime you clean but I guess it wouldn't hurt.