I have the same year and model. The treble pot has a point around 2 where it goes from no treble to plenty of treble in a quick rush, then from 3 to 10 it is a very fine adjustment. It is a little less subtle in series mode than in parallel.
As for the set screw, you could try a small amount of Liquid Wrench on it, wait for it to penetrate, then put the screwdriver on and
gently tap it with a small hammer, that might loosen it up. If worse comes to worse you can always buy a new pot and/or knob from G&L.
http://www.glguitars.com/shopping/sh...d=22&cat=Knobs