[Oblio13]

If there's any oil soaked into the wood, soak the toe of the stock in acetone to remove it. Then drill a small hole (which will be hidden by the buttplate) right into the crack. Fill it with expanding polyurethane glue, like "Gorilla Glue" brand. Clamp it and let it cure. Use a block plane to flatten out the spot with the chip, and glue on a piece of walnut cut so that the grain is running in the same direction. Once that cures, shape it.

Strip the stock with a stripper like "Citrisolve". Steel wool everything thoroughly. Use a stain and a Q-tip to "paint" lines that follow the lines of the grain and hide the splice. Give everything a few coats of penetrating Danish oil, and finish it with a few coats of Tru-oil or Tung oil. The finish will look better than it did new, and the repair will be almost invisible.

 

[Oblio13]

Yes, just dip the cracked part of the stock in a container of acetone and let it sit for a bit, until it penetrates the wood. It'll leach out the oil so that the glue will stick.

Then drill a hole from the rear, i.e. under the buttplate, not quite directly under where your screwdriver head is. Drill directly into the crack and follow the crack. The hole is not for a screw, it's a reservoir for the expanding urethane glue, which will fill it and expand into the crack. You can also gently pry the crack apart to make sure there's glue in there. Then clamp or rubber-band it together until it cures.

The chipped part won't be hard to match, it's plain straight-grained walnut. You can stain or bleach it to match even better, and then you can use stain to "paint" grain lines that will hide the splice. Expanding urethane glue will be stronger than the original wood (if you do your surface prep and get the oil out, of course), it will leave no voids, and it will be easy to steel-wool off the parts that show.

Then refinish the stock. Another easy job, since there's no checkering. Don't even do any sanding. Just use a plastic scraper to take the old finish off after it's been softened with Citristrip, then steel-wool everything really well.

 

[Oblio13]

You are getting some great advice in this thread, and some less-than-great advice. Now you have the dilemma of sorting the wheat from the chaff. Good luck.