You can bake a ball and get most of the oil out of it. The problem being, that most newer covers are sensitive to temperature extremes and can crack. Also, during the heating process, the ball can loose plasticisor (the chemical that makes it hook).
A safer method would be to have it resurfaced to restore the surface, and use Hook Again treatment (24 hour process) to restore the chemicals in the cover. You can also use a bucket with warm (not hot) water and Dawn dish soap.
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Bowler's World Pro Shop