by Paul_C » Tue Dec 19, 2017 7:33 am
It looks like you might struggle to get much glue in there, unless you can open the crack up.
If I was asked to do it for a customer (I repair guitars for a living) I'd be looking at whether it was possible to get glue in first.
If so then the best glue is usually Titebond (in this case probably watered down a little to give it more chance of getting into the gap) and because of the difficulty of getting it in, I'd be using a syringe to try and force some in after taking off the tuner on the end to push the needle into the gap where the hole (even a very small needle is likely to be wider than that thin crack) can be covered up.
If you can find a way to get some glue in then clamp it up for an hour and it'll be fine, though as that might be difficult you could probably leave it as it is without too much to worry about, and just keep an eye on it to see if it widens at all.