It's grease? In that case, you upped the level of waterproofing on that item without spending any extra money or work. It's not a stain, just even more waterproofing. :d :d
Klim has a product that they call revive-x, this is available thru any klim distributer and it is a spray on treatment for there gore-tex gear to redo the water repellancy of the garment as stated before a being washed a few times the water repellancy will start to be not as effective.