One thing I have noticed about the S120 is the tolerances are really tight. Which is good and bad. As the parts wear, they fit better and better but it does make for a little more effort when assembling the kit.

Try opening up the large holes in the T bar that the pivot sockets fit into. Do this with some sandpaper and to a little at a time until the pivot ball sockets fit into the hole with out having to force them in. Take off a little at a time. Remember, you can always take off more but you can’t put it back. Do this until the pivot balls are free and smooth with the two screws in place. You may have to trial fit several times until you get just the right amount removed. Also, do not tighten down the two screws real tight. I just use my thumb and finger and tighten them until they are barley snug. It’s a feel thing. They will not back out as the screws are going into plastic/delrin.