I have broken both of my mounting clips more than once.  I successfully =
glued the pieces back together a few times before I realized a more =
rugged solution was necessary.

  The usual failure mode is that the clip splits in half between the two =
ears/tabs that hold the speaker in place, leaving those tabs intact.  =
What has worked best is to realign the two broken pieces back in their =
original alignment on a piece of wax paper or aluminum foil.  Cut a metal =
(1/16" aluminum plate about 1 1/2 inches by 2" ?) to fit between the =
tabs, trim to fit so that it doesn't hang over the edges and drill holes =
in it to line up with the original mounting holes in the plastic clip.  =
Mix up a batch of epoxy, apply to the broken edges and push them =
together, then smear over the surface and push the metal re-inforcing =
plate into the epoxy, aligning the holes in the plate with those in the =
plastic.  Allow to cure and re-install.

Harvey