From my limited understanding the neck adjustment only goes cw (never ccw) and most likely the truss rod is jammed or the threaded part of the rod/nut is stripped. The repair involves cutting out the 1st fret to access the the square nut embedded in the neck under the 1st fret (if you choose to save the neck to keep the originality ) this is not an easy process but it can be done. You can chase the threads on the truss rod if it is salvageable or replace it, and the same thing with the nut. If you go to this extent do a fret job too. I have a 1990 sss strat that I love and have a replacement srv neck and it is still sitting waiting for me to make a decision on a new neck The best of luck to you no matter what happens.