When I was working in the UK as a gunsmith apprentice, we dealt with a lot of oil soaked stocks. Our method was to use a heat gun and wipe the oil off wiht a acetone soaked rag as it bubbled to the surface. You have to be careful not to scorch the wood, and work in a well ventialted area it'll smoke a room up fairly fast. Our boss swore by Tricoethylene, soaking the whole stock in it over night. I refused to use it though as it is apparently highly carcinogenic. I have also heard of using the hot blue bath and immersing the stock in that, apparently the wood comes out white and completely oil free. That's third hand info though and I would tread very carefully if thats something you're inclined to try.