Is the socket head of the screw stripped?

That is, does the proper size allen wrench just spin in the hole and the screw won't budge?

If yes, then the screw can be CAREFULLY drilled out.

If you want to get fancy, take an old screwdriver and grind the tip so it fits in the socket screw hole.

Heat the tip of the repurposed screwdriver with a torch (or gas stove) until it is almost glowing.

Hold the hot tip of the screwdriver in the socket screw hole for 2 or 3 minutes to soften the loc-tite and then IMMEDIATELY drill with a properly sized REVERSE drill bit.

Screw should back right out unless it has been cross threaded in the sight body, in which case, drilling is probably the only remedy.

John