I repair and restore older (much older) enfield stocks with just that same damage. Here's my tuppence worth.
That guck looks like old varnish or shellac to me. Is it hard and crusty, will it chip and scrape with a knife?
Stay away from oven cleaner on wood, it is nasty stuff and can do damage (this is the voice of experience here. Bindar, dundat!). It also has a tendency to bleach and change the colour. Saying that, I have used it and it works very well, but only used it as a drastic measure on a oily old stock that looked as if it had been used as a baseball bat then as a dipstick for a septic tank. Cleaned it right up but took it down to 'new' looking wood (my stock turned colour with a slight green tinge, I had to dye it back to brown). The concern is the lye in it can be residual below the surface and would continue to eat at the wood in years to come. But hey, if it is a beater of a sportered stock, have at her. It is all a learning experience, and we can only learn from our own mistakes, unfortunately.
My prefered method to get that shiiit off would be with paint stripper. Don't go for the heavy duty industrial strength superduper econo stuff. Pick one of the pricey ones that is good for antique furniture, it wont harm the wood and will leave the 'age character' or patina unharmed. If it is gentle on wood, it will be a selling feature and will be emblasoned on the can.
Oh ya, buy rubber kitchen gloves, a couple of cheap stiff brushes and some dish sponges with the rough scrubby on one side. A paint drip tray would be handy to have too. Follow the instructions on the can to the letter, don't let it get on your skin or in your eyes. It can tickle a bit and tastes like crap.
When done wash the stock quickly with hot dish soapy water in a bucket and then paper towel dry it real quick. Don't let it soak up too much water, things will swell, distort, open up cracks, all kinds of wet problems. Hang it up somewhere warm, just leave it alone overnight to dry gently.
The crack I too believe was caused by somebody cranking the stock bolt in too far for whatever reason, although it looks pretty stable now and hasn't moved around much. The wood is susceptible to cracking right there, that metal tie plate was designed and installed for that very reason.
Clean the crack out with acetone or laquer paint thinners, slop lots in there (a syringe with needle works great for this). Epoxy works great if you can get it right in there, or, super glue in this case will wick down inside the crack due to its 'water like' consistancey. Cyanoacrylate is the magic ingrediant, it isn't too fussy about oil or grease either, just as long as it is fairly clean, it will work. Set up your vise, clamps or whatever, do a test clamp and get it ready. With cyanoacrylate, you have only ten seconds to get it set up and clamped, then she is stuck!
I have found that it holds fast, and if the wood breaks again, it will break right beside the glue seam, not on it, proving that the glue is stronger than the wood.
Let sit for 24 hours before shooting.
