I foound 2 chemicals that do work to remove marks and burnt in fingerprints and such rather well from the rubber part.

1. Ecosense Tub & Tile
2. Concentrated Goo Gone (which by the way is certified by and used by Apple when re-manufacturing/refurbishing and in apple certified repair shops). As for the little ding i would have to say lightly use a black silicone sealant
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