Hmm, thanks guys.
Great find Dave! I'll chase that one up,
but it sounds like the Loc-tite solution is for metal -> metal threads. My inserts are plastic. Failing that, I'll give the bigger screw a go. In the meantime, I've just moved my strap to the back setting.
All I have to do now is find a new boom.

edit: just re-read the starboard site
really does permanently restore the threads in stripped out plastic inserts, such as the footstrap insert threads