Richard - sounds like yours has something to get hold of - mine is inset if anything , so 'grabbing' it is not an option unfortunately.
Sorry to hear that - just assumed it was the same as mine. Maybe not posible to cut a screwdriver slot into screw head with junior hacksaw either, which would have been another possibility.
Nothing less than brazing something to the existing head would allow enough torque to be applied to remove it. The heat required would create an awful mess though.
Given the fragile nature of the headlamp therefore, drilling or grinding off screw head (with suitable Dremel bur) is the only option I can see working.
