>
> How about epoxying a washer in the appropriate spot?
>

Oil the screw lightly but thoroughly (use a modeler's paintbrush or
toothbrush).  Pour THICK superglue (cyanoacrylate) into the screwholes (do
it a screwhole at a time), allowing the glue to fill the cracks, then screw
the screw in and allow glue to set thoroughly... give it hours.  Remove the
screws... they might resist a bit at first, but the glue should have
"remanufactured" the threaded holes.

Alternatives:
1) same process, using polyester or epoxy resin
2) insert oiled screws; THEN carefully melt plastic around hole to soften
thoroughly full length of hole; then carefully squeeze melted plasctic to
reform and fuse around screws

--
Regards
Andrew Grebneff
Dunedin
New Zealand
Fossil preparator
Mollusc, Toyota & VW van fan