The volume pot of my old JMP-1 is very scratchy and noisy so I would like to spray some switch cleaner into it. I tried to open the chassis. I have unscrew the 3 rear screws but nothing happened; I also have unscrew the six little screws on the golden edge (top & bottom) but nothing happened: it seems glued. How to open the JMP-1 chassis? Can you help me?