WHAT??!! YOU MEAN YOU HAVE TO ADJUST THE SIGHTS ON THAT FAL??!! INCONCEIVEABLE!!
Geez, I was recently led to believe that the FAL was the absolute epitome of rifle development, WAY better than the lowly AR could ever hope to be, the AR doesnt even qualify to be on the same rifle rack, yada, yada....
Ya wanna borrow a bigger hammer?
Just kidding. Hey, gentle heat and a properly fitting screwdriver have gotten me out of some tight spots before. Heat also works to soften loctite, if that's the problem. Fitting the screwdriver to the head of the screw and rapping the driver handle with a mallet a few times will sometimes loosen up a tight screw as well.
Not to be a smart aleck but have you tried loosening one side and then tightening the other. The FAL rear sight is a sort of pusher arrangement. If you want to move it left you loosen the left side screw and then tighten the right side screw.