I work on machines in textile mills. Some machines are old. Lots of rusted in Allen head screws. We have 2 things we do before drilling them out. One is to hit the top of it with a hammer, this helps close it back up some. The other is to drive a torx socket into the Allen hole. This is the method I use the most. Hope this helps. Noticed the ones on the fans seem to give problems from reading through several posts.

 

Hitting it with a hammer also helps relieve some of the hate towards the guy who stripped it out in the first place..... I've used the torx method allot, ez-outs, reverse drills, liquid nitrogen and heat.