While hanging our faux brick panels up in the playroom/guest room I happened to look down and see the grotesque window tracks. I remembered that I hadn't cleaned this particular window when we moved in over two years ago, since this room wasn't going to be used that much.
How to Clean Window Tracks: white vinegar and baking soda (or hydrogen peroxide!) 30 Q-tips toothbrush hot water paper towels Sprinkle baking soda into the corners, then pour in some vinegar. The baking soda will begin to bubble and loosen up the cruddy stuff. When the bubbling calms down, begin to make circle motions with a Q-tip, then go back into the corners and sweep the muck towards the middle. Pour warm water from the corner to the center. Use your paper towels to wipe everything dry.