fixitagaintomorrow said:Get a dremel or cheap facsimile thereof.
Cut a slot in said bolt head.
Use a ratchet with screwdriver bit in, exerting a fair amount of pressure straight down onto the bolt head to undo.
When it starts to come, work it in and out as you undo it.
I sympathise, these little torx screws in the tb can be a proper bitch when they get stuck.
I had to do this, took about 30 mins. Its the only way, why couldnt they use allen keys instead of torx screws!