It's easy to fix.
Disassemble the gun. Mainly, the tang, barrel and lock should be removed. I also removed the trigger, but it wasn't really necessary.
Go to a hobby store that sells radio control airplanes or radio control cars. In the glue section they will have cyanoacrylate glues (Super glue) But this isn't the same super glue you buy at the grocery store or even the hardware store. It comes in 3 different viscosity - THIN (blue cap), MEDIUM (purple cap) and THICK (red cap). Hobby stores call it CA (see aay)
You want the THIN. The stuff is like water or rubbing alcohol in viscosity.
Mask off the stock with blue painters masking tape. You DO NOT want this stuff going anyplace except into the crack. Mask right up to the edge of the crack. Get the tape within 1/32" of the crack, then mask off the rest of the stock.
Get some of your wife's extra-strength fingernail polish remover or even real acetone. Get a cotton cloth or some cotton balls.
Unscrew the needle tip from the bottle of CA and cut the tiniest hole you can get. I use an exacto blade and shave off a tiny bit and then check to see if there's a hole yet. Go slow, you only get to do this once and too big a hole makes this VERY difficult. Once you've got a tiny hole, screw the needle tip back on and put the cap on the bottle. Basically, cut it open like a tube of caulking. But the hole needs to be the size of a needle.
The reason you take the needle tip off the bottle, is because you'll have a tendency to squeeze the bottle while gripping it and cutting the tip off. When you finally get a hole in the tip -- SQUIRT -- right in your eye! Trip to emergency room - intense pain - nasty burned eyeball - don't do it. Take the top off when you're cutting the hole. Trust me.
Put your CA in the refrigerator for about 45 minutes. The cold makes it even thinner. I know it sounds weird, but it works.
When you've got the CA good and cold, take it out and put the tiniest few drops into the crack. The stuff runs like water and it will make an AWFUL mess if you squeeze the bottle. Let the drops come out on their own. Be gentle.
When the CA hits the crack, the stock will soak it up like a sponge. It wicks into the crack and flows evenly. Depending on the length of your crack, it might take 3-5 drops to "wet out" the entire crack.
Have the fingernail polish remover or acetone handy, and a willing assistant if you can find one. SOAK the cotton cloth or cotton balls in the solvent and wipe any excess off the crack immediately!!
It sets almost instantly. I would not recommend this if you were trying to glue 2 pieces of wood back together, because any misalignment when sticking the pieces together = a ruined piece. It sets up so fast you have no time to align parts. When the parts make contact, it's done. But for cracks in wood - this is liquid gold!!
It sets fast and dries in a few minutes. I'd recommend you glue - wipe off excess with acetone and then immediately remove all the tape. Check for CA that wicked under the tape and wipe off immediately.
DO NOT use paper towels to wipe off spilled glue. They make a terrible mess. Use an old cotton t-shirt or cotton balls soaked in acetone or extra-strength fingernail polish remover.
I've been shooting mine for over 2yrs and it's held up. You can still see the crack, but it hasn't cracked anymore.
Hope this helps.