If it's the lower one, you should be able to grab the head with a small pair of Vice-Grips. If it's the upper one... (this is going to sound pretty "Neanderthalic"...but) you can use a cold chisel and strike it on top of the head in a counter-clockwise direction. You probably wont find a cold chisel long enough, just put it in a socket and put a long extention on it. It should break it loose enough that you can use what's left of the eaten-out Torx to remove it the rest of the way. "Aero-Kroil" is the best available penetrating oil for hard to remove parts. Replace the (Lame-A$$) Torx-heads with standard hex-head bolts.
