was it a Torx27? Did you use a Torx 25 by mistake?I'd try to tap a larger bit into it and see if you can get to it. I'd try Hex wrenches to see if there was one you could use to get enough grip with to break it loose.If all else fails get a schitload of masking tape, triple mask off the cover then take a hacksaw blade and make a slot in the screw head to use a flat bladed screwdriver with. Sometimes a chisel will do the trick if it is soft metal.IF you have air tools a whizzer wheel will make quick work of cutting a slot, remember lost of masking tape t protect the chrome cover. Another way is a hammer and chisel being used to tap the bolt loose in a CCW direction from an outside edge. A little heat from a soldering iron might loosen any loctite that is on the bolt, just hold the iron in the center for a couple of minutes then try whatever tool you choose to rotate the bolt.