I used nail glue, but it was the gel type. I applied it in between the crack and then outside and inside the dome where the crack was. It works like new!
I don't know where you can purchase the glue anywhere else but I got it in an artificial nail box. I can't seem to find it anywhere else, and I really like it too. You have to purchase the more expensive artificial nails, make sure to look inside the box and double check that it is a gel glue. It should look kind of like a super glue tube, but with a blue-ish green hue to the outside design.
Hope this helps anyone! ;D