I just repaired a very similar problem...I don't think there is a water problem. If you feel along the underside of the loose enclosure, you will probably feel double-sided tape. That appears to be the only thing, besides the plastic rivets, sticking to the wall. I tried to tear off as much of the tape as I could and injected Liquid Nails tub/surround adhesive. I crewed in 4 short, self-tapping screws and braced it with wood for about 24 hours. When I took the bracing off, everything seemed good as new. If you don't like the chrome looking screw heads, you could always paint them to match.