If it's really soaked bad then I'd do all those things mentioned here. First I'd heat it to draw the oil to the surface and wipe off with paper towels and cheap alcohol. Then heat it some more and spray K2R on in it. I'd repeat the K2R several times. When you've got it as good as you think your going to then I'd use Balsarite on the oil areas before trying to cover it. I'm sure there is a point where it would be easier to just replace some of the wood but that would be a judgment call on your part.