The Chinese stock on my MAK-90 is cracked.  The original owner put this on many years ago. Looks like maybe he overtightened the tang screw. 
It's strong enough to shoot, but these two little cracks are annoying. 
And I don't want it to get any worse.  The cracks temporarily open slightly when I put 3-4lbs sideways on the buttplate. 

Is there an easy fix for this?   I don't want to spend a hour working on it, and then discover that I used the wrong technique or wrong glue. 

If I could find a replacement for $50 or so, I'd just buy one.  I couldn't find one at DesertFox, Gunbroker, AKfiles... 
There's one on Ebay for $175, but I ain't gonna pay that!  
Attached File

Wood glue plus a brass screw or two.

I fixed one like that a while ago.  I gently pried the crack open and dripped super glue into the crack.  Let it run down inside, then clamped it closed overnight and it's holding up well.

Use hot hide glue, since clamping would be an issue. Or use modern glue and a piece of threaded steel/brass to clamp and reinforce internally.

I'd use the hide glue.

OP... Fixed one like that last year. Check luthier supplier for this glue & whip tips for precision gluing Here. The different thickness of the glues and the tips for the bottles allow you to put the glue where it needs to be and not where it shouldn't go. It's best to try to figure out the angle of the cracks thru the wood and then drill a small hole down the length of the crack that will allow you to flow glue or epoxy into the crack from beneath the surface so you don't make a mess of the finish. Drill from the tenon end of the stock that fits up against the rear trunnion down the long axis of the stock trying your best to follow center of the crack.

Here's what I did... Drilled a small hole (1/8" in. IIRC), the hole should be a bit larger than the brass stock repair screws used later the length of the crack and used a hobby knife blade to gently pry open the crack to let the adhesive spread as far as possible into the repair. Used wooden toothpicks placed in the flexed open crack to keep it open. Mixed up some Devcon 2-ton epoxy and using a piece of rod stock and compressed air in a can started to put the epoxy down the hole, the compressed air was used to force the epoxy to spread throughout the crack. Be careful not to overdo it since when you clamp up the stock to close the cracks you don't want any squeeze out if you can keep from it.

Next I coated some threaded brass stock repair pins I got from Brownells in the epoxy and using some wood clamps (made by Irwin IIRC, the kind with the ratcheting pistol grip, blue in color) and wax paper to keep anything from sticking. Wrap the stock in wax paper in the clamping area and push the brass stock repair pin into the hole with a pair of vise grips. The epoxy will dry around the threaded brass stock repair pin locking it into place and strengthen the area. Allow everything to dry for 24-48 hrs.

Remeber the glue and tips I mentioned ?? Break those out and some clear scotch tape. Use the edge of the tape to follow the edge of the crack, making a small dam in case you use too much glue. The reason for the clear tape is so you can see thru it to get as close to the crack as possible. The glue in the link is available with a orange-ish tint, which is what I used, flow the glue into the remaining crack until it's level with the stock surface. This should completely seal the remainder of the crack. If done correctly there should be a small line of glue that stands up just a few thousandths from the stock surface. Using a brand new blade in an X-acto knife CAREFULLY scrape the line of glue to remove the surface gloss and bring it level with the stock surface.

Not an easy repair and quite tedious to do but if you get it right the factory stock finish is virtually untouched and the repair resembles a line in the wood grain and blends quite well. Just cut the part of the brass stock repair screw sticking out of the tenon part of the stock off and hand file it flush with the stock surface. This part of the repair will be hidden when the stock is mounted back onto the rifle.

Bonus points if you save the drill dust and measure the brass stock repair screw and cut it just a bit short so it sits below the surface of the stock when pushed in, then mix the wood dust into some glue or epoxy and use that to top off the hole making the repair almost invisible unless you know where to look.

Crack repair video

Or place it in the capable hands of Z-recto and let him work his magic on it...

This. Wood glue is the right glue. CA type adhesives are strong but tend to be brittle like glass. They work best on glass type substances. 

Wood glue

Replace with a new one!