I've a plastic cold water filter that is some 150mm in diameter and is
assembled using eight 4mm dia self tap screws. Five of the screw
holes have partially or totally stripped their thread, not so much due
to abuse - possibly in the original assembly though (!) - but I think
due to an over large hole existing in the manufacture for the pilot
hole.

The plastic is hard but I is I think thermoplastic rather than
thermosetting - what suggestions are there for a solution ?

There is not enough material to drill and plug - I could go up a screw
size but buying in a small number of SS screws is not preferred at the
moment.

I have thought of spraying the screws with silicon, filling the holes
with epoxy and then putting the screws back in. Would this work ?
Once reassembled I think is unlikely the assembly will be taken to
pieces again.

Thanks

Rob