Since the action is fine and the neck angle is still good, then if you can get a thin finger nail file in the crack (if you can open it up) and clean out the old glue first. Take a feeler guage and use that to help get the glue in the joint and clamp it. Don't over clamp, you don't want to damage the guitar. Titebond glue is best for this or a good quality carpenters glue if you can't fine the Titebond, (Red cap) is best.
Dennis
Dennis