I don't recall seeing this thread before, but before giving up, ohm out all the PWB traces while flexing the board, to find cracks. Double it up with wiring if necessary. Also, for sure, use some contact cleaner on R18 (variable resistor). These are notorious for getting dirty/noisy after a while, particularly when used in this sort of "open" arrangement. This should be a simple fix and any/all of those components should be available or repairable.
Brett