I have done this over with Brunswick Pro-Active coverstocks several times. What I do is use hot water, not boiling. If you ever had the zone stocks when they had oil in them placing your hand on the ball caused the oil to migrate to the surface. So extreme temperatures are not necessary, therefore not endangering the core at all. I add a little Dawn dishwashing detergent and soak for about 15-20 minutes. The water gets quite dirty. The ball goes back to it's original color and performance. I have never taped the finger holes because I wanted any dirt in the holes cleared also (i.e. tape residue, oil, finger dirty). I never noticed any problem with the ball after cleaning so I don't believe any core damage was done, but don't doubt that it is possible. Especially if the inner material gets wet wicks in and then gets cold or hot. The material around the core looks to be much more porous than the outer shell. I don't seem to have the same trouble with the new Storm Coverstocks, but I had to do the this a couple of times a season with Brunswick and AMF.