I just bought one off the classifieds and when it arrived, it had the same problem. Didn't have it when it was shipped.
I used a 2 component Loctite Epoxy Plastic Bonder and a small hobby clamp and it appears to have worked fine. Although I haven't field tested it.
Be very careful of any glue that seeps out on the inside, as it is very close to the side panel. I put blue painter's tape on the side panel in the area where it was being glued. If I had not, it surely would have bonded, as there was a small amount of seepage when clamped.