Fairchild 670 Threshold Leakage - Wont Unlink

Hello, we have a 670 that does not allow for independent operation of the thresholds. When adjusting Threshold 2 CW (lowering the threshold) Channel 1 is also reduced when not in stereo link. Oddly enough this does not happen in reverse order, Ch1 does not affect Ch2. All tubes have been replaced, and some caps have as well, although many of the black and wax paper caps remain in use. Anyone here intimately familiar with the circuit that could shed some light on this schematic as to what I should check for? I am not very familiar with Vari-Mu circuits.

https://sites.google.com/site/atvmagoo/fairchild670-Blueprint-a.jpg