I would take it up to the Sprint repair store... it shouldn't wobble that much... while it DOES slightly after use and "loosen" it up, it shouldn't wobble to the point of annoying you. I have used the Sprint rubber case, and tried the Otterbox commuter and no cover is really going to help with the wobbling, as the case has nothing to do with the sliding. They can try to fix or tighten it at the repair store. When I had an issue with my screen, they were actually able to replace my screen on the spot. good luck!
PS - DO NOT GLUE YOUR PHONE!!