Acetone, with or without the Whiting. If you don't use the Whiting, you should be ready to rub off the acetone with a cotton rag. On short stocks, I have used one of the large heavy tinfoil turkey roasting pans that you can buy in some grocery stores. You will have to bend it a bit to get it so that the stock fits into it. Cover the gunstock halfway with Acetone, then seal the top over with some tinfoil to slow evaporation. Unwrap the pan every half hour or so and turn over the stock. this removes old oil, sweat stains, all the finish, and some wood stains. Any stubborn areas can be scrubbed with a nylon brisel brush. Air dry it thoroughly after the soaking and then completely refinish it.
This method is the only way I have found to allow me to glue repair cracked stocks. I also use it to remove old oil from the head of an old stock before I Acra Glas it. You have to get all the old oil out before you can make repairs or glass in a stock. Bob