BigJimP said:
I think I'd stick with standard woodworking ( aliphatic resin glues ) like TiteBond II that is waterproof. I wouldn't thin it out either / but you can use a needle tip injector to get the glue into the cracks as deep as you can.
The aliphatic resin glues also have very poor gap-filling properties, even when not thinned. The strength of the bond made with these glues depends on getting the two surfaces to join tightly, and using quite a lot of pressure when clamping. If the joint is open, the glue itself has very little structural strength.
Cracks in wood are usually due to shrinkage, and they seldom want to close nicely. If you use a good structural epoxy, it makes a strong repair even when things don't go back together as tightly as you'd like.
Wedging the cracks open a bit is a good idea (make thin wedges from a hard wood like oak or birch, and tap them in
gently with a hammer); so is using a needle injector... You can thin some of the epoxy slightly with denatured alcohol to get some deep in the crack this way, and then thicken the rest with wood dust and work it in with the spatula to fill the void as much as possible before clamping. (Use an epoxy with a loooong pot life -- the slower-curing it is, the easier all of this will be.)
Going just from the grain pattern, it looks like that stock might be walnut under all that paint. If so, stripping it might not be too bad, and who knows... the wood might be kinda purty.
ETA: Repair the cracks
before stripping the paint. Getting stripper and paint sludge in the cracks before gluing is another great way to guarantee a failed repair...