Another vote for wax.
With oil, you are not supposed to get it on the wood. Wax will protect the wood just like it protects metal. So you can remove the stocks and wax them, wax the butt frame, put it back together and have no worries. If you don't use wax but instead put oil on the butt frame, the oil may soak into the wood. I've never had a problem with that but you often hear about "oil-soaked" stocks.