I had mine DA L 18-55 dropped too and the screw threads dropped off, the AF wasn't working because of that.
Today I had an DIY idea and it works!!
1. the plastic sheets cut off from some cheap packaging plastic
2. punched a holes wide enough to push a screw through, but tight enough not to let the head of the screw to pass through
3. tighten the screws - the plastic just holds the mount and the screws close together, it's thin enough for screws to go in and dont scratch the camera mount and it's softer than metal so it can't damage your camera
Tried it, screwing the lens on is a tiny bit harder but thats expected, and it works like a charm
I know some of you broken the whole ring, but if you manage to superglue that plastic and make this you have your cheap reserve (or even main) all-rounder ready to serve
Cheers