Originally Posted by Dakins
The metal might just be starting to oxidize, try using a stain-removing brass cleaner. In my opinion, the very best product in this category is Twinkle.
It works for polishing your stem as well. You can also try soaking the windcover in a mixture of salt and vinegar for a little while. Careful, it's very abrasive.
it doesnt really look like oxidization but ive never seen brass in the early stages of oxidization, and its only at the top closest to the coals not the bottom