I like to start cleaning gun stock wood with something mild like Murphy's Oil Soap or dishwashing detergent. For wood that is oil soaked, I like to start with absorbents such as whiting or kitty litter, with gentle heat to help bring the oil to the surface. I have also found that a solution of household ammonia does a great job of removing old grunge and skin or gun oils that are on the surface. Ammonia turns oils into a soap, which then can be rinsed away with warm water. But remember to rinse off all ammonia residue completely because it can damage wood. I only resort to soaks in organic solvents such as acetone, lacquer thinner, etc. as a last resort. These harsh organic solvents will absolutely damage the cellulose and lignin structure of the wood, so soak times should be kept to an absolute minimum. Kutter's advice to go slow and easy, and to be very patient is priceless. The oil did not soak deep into the wood in a short time, and it will not come back to the surface in a short time either.
Oil removal will always be a compromise, and I do not believe that it is possible to remove all traces of oil that has soaked deep into the wood without causing even more damage to the wood. I learned this the first time I set a stock aside for a month or so after I de-oiled it. When I finally got ready to apply finish, I noticed that my nice clean wood had dark oily areas again, because the oil deep in the wood migrated back to the surface. The best we can hope for with deeply oiled wood is to arrest the damage and stabilize things before the wood becomes punky or rotted. I do agree with Geo that your forend wood does not look deeply oil soaked. But pictures can be deceiving. I'd be very cautious about sealing the end grain with CA or epoxy because any that gets on the exposed surfaces is going to affect the even penetration of any stains or stock finish you use. I won't repeat all of the reasons I prefer to use Titebond II wood glue versus epoxy when you are able to get most oil out of the wood, except to say that properly prepared joints are stronger than the wood, and it gives me a more invisible repair than anything else I have used. Of course, the crack shown at the butt end of your forend may not appear on the exposed surface.