For deeply oil soaked wood, the solvents such as acetone, alcohol, or lacquer work well. If the oil and grime is on or near the surface, common household ammonia followed by Tide or Dawn detergent does a good job. Ammonia mixed with oils and fats creates soap, which of course rinses off with hot water. Sometimes you can get away with a partial soak of just the head of the stock in stronger solvents. Common isopropyl rubbing alcohol will remove the finish on many older guns, so they may be shellac or something else that is alcohol soluble.
