thanks kirk, that's what i've done.
hope it holds up for a little while.
after some looking at it, there are four tabs - two on the top near the outside, one in the top corner and one towards the bottom of the assembly.
looks like the previous owner glued the one on the bottom. the one that broke on me was in the top corner, leaving the two outside ( and the little dot between them).
well after playing with it, i was able to get the two outside to lock and i guess the pressure from the dot seems to hold it. but it was still a little flimsy. so i got out the glue and added it at the bottom ( there's a little lip that contacts the back of the reflector ) and put it bad together. wouldn't you know it, i snapped off one of the good ones!
but for now the glue seems to be holding *crossed-fingers*