I too have used acetone to remove oil from stock heads. Many times i have seen people cleaning shotguns, and squirting oil into the firing pin holes in the breech face, thinking they are doing good in maintaining their shotgun.
Recently i was given a nice old sidelock side by side, the stock head wasn't too bad with oil, a relatively quick soak with acetone did the trick. I have used this method several times and never had a problem with cracks, unless the acetone had caused previously glued splits to reappear.
Some people in this thread have mentioned using oven cleaner, if an oven cleaner contains caustic soda (i am not sure what its called in the usa) it will darken hardwood including walnut markedly.

Last edited by bonny; 07/12/16 10:08 PM.