I had a problem with my windwings vibrating loose as well - solved the problem with a little Permatex LocTite (blue I think). Haven't had any problems since... I suspect this will work as long as you have at least a little 'bite' of thread left - worth a try before you drill, tap and if it's a bad day - replace the glass in the windshield!
I've also used this trick on those pesky wiper arms that tend to work their way off the splined shaft. I can still take the off if needed **rarely if ever need to remove them... - but they don't come loose as you are cruising down the road.
If someone wants to hear a good story - - ask Ed Combs (DV) about his unique solution to the loose wiper arms
