PLEASE, PLEASE, PLEASE wait for more knowledgeable responses before you try this method, but I have had some luck with wrapping aluminum foil around an eraser and gently rubbing away the oxidation. Using oil would reduce friction further, and serve to protect the underlying precious metal.
Again, I offer this as a suggestion, but wait until someone with actual conservation experience endorses it, or offers something far more sophisticated. I would hate to see you ruin your piece.
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