Jerry,
You need a quality short, sharp and stiff allen wrench for mod screws......if the wrench is twisting you are more likely to break the wrench itself.
For god's sake don't use a ball end wrench......they suk.
Give it a little drop of wd40 or break free or something like that from the backside and let it sit for a while.......then using a quality wrench set(no long T handles......not enough leverage, and not those crappy $3.99 pocket sets)
I like the good sets you get at the hardware store with the heavywide plastic handles. If you can't get enough leverage onthat screw to move it I'm not sure what's going on.[:-]

You'll never win with mod screws ever........1/2 think they are too loose and should loc-tite'd in, the other 1/2 cay they're too tight and they can't move them?(Then there's me who never seems to have any problems at all with any of these stinkin things wondering if Jerry didn't use an impact wrench to tighten them the last time.)

Don't panic Jer, you'll get em'.