More likely, the entire rear hatch inner trim panel is falling off. The brake light cover is just a piece of this. There are 4 clips at the bottom, and 4 snap in pins at the top. There is also a rectangular surround for the handle, that snaps straight out though requires some force.
The pins go into sockets in the panel that are probably all broken out. Volvo has this problem with every 745, 945, 965, 855, and V70 and doesn't address it properly. People also commonly crack it as they load cargo.
The fix is a small repair kit that includes a couple of new metal plates to reinforce the cracked areas, plus self tapping screws for installation. This makes the whole panel reattach to the metal of the hatch the way it's supposed to.
FCP Groton may carry them. (www.fcpgroton.com) You may also get them through your local dealer, or another online source like IPD (www.ipdusa.com) or Volvoworld. My friend carries them at Eurocars Plus, (www.eurocarsplus.com) if you can't find them elsewhere.
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Rob Bareiss, New London CT ::: '87 244DL/M47- 221K, 88 744GLE- 202K, 91 244 181K, 88 244GL 145K