Originally Posted by sobemtv
The crack is not bad. I may try to inject the glue.
And here are the questions
1) what glue I should use?
2) how can I inject the glue? I don't want to remove the fingerboard as I do have confident to do that.
First off, don't do anything to the neck if you're ever hoping to send it back to the person you bought it from. The second you do, it's yours, no matter what falls off it a year from now.
Any wood glue should do. As mentioned, you'd probably want to gently pry it open as far as you can without making it worse or breaking something. It will also tell you how good or bad the rest of the join is on that fretboard.
You can get throwaway glue injectors at Woodcraft or a good hardware store. You can also use a hypo for children's medicine or just push it into place with a flat stick.
The trick is to make sure there's glue covering the entire surface you want joined (something I suspect was the cause of your original problem) so that it smushes out when you clamp it down.
If you're unsure about what you're doing, I'd suggest just doing the exchange and moving on. If the seller tells you not to bother sending the old one back, then you have something to experiment with for free. Good luck.