Solution???-drill that puppy out and get a shim to place under the sight and mount the sight like it should be.
no screws etc hand fitted and it will not move unless you drive it out.
drill out the set screw from the sight, drill the hole larger and tap it to an american threaded screw.
About the best solution would be to get a torx bit that's a bit too big for the hole and hammer it in. you may also want to heat the torx bit to get the heat to transfer to the screw and put a dab of beeswax on it. That'll break any loctite that may have been on the threads.
Finally got my williams fire sight installed love them, after breaking multiple drill bits i took my cutoff wheel cut the rear sight through the set screw just about all the way through then took hack saw and finished last little bit