The industrial strength ammonia, I think it's called anhydrous ammonia, will remove oil. It's the principal agent in oven cleaner.
I used oven cleaner on a military stock that was oil soaked. It leached out the oil, at least most of it, but left the wood in a state I don't think is good for a high grade stock. It was fuzzy and still a little oily.
Anhydrous ammonia is available at your hardware store, but it's nasty stuff and needs to be disposed of properly. It's a good solvent for cleaning guns, but I don't trust it undiluted even on steel.
