I used a product called (super) IRON-OUT rust & stain remover. Powder in a bottle. USA 1-800-IRONout maybe also for Canada.. http://www.summitbrands.com/brands/IronOut.aspx found at Ace harhdware and other stores./ MIx a small amount with water and rub with a toothbrush or something.
++++karma to the posts above me. i also have some stains to remove, ill have to try that.
for those of you that have ever got grease dripped on them from the chairlift, i used dawn degreaser dishsoap and it worked like a charm even on thick grease.