Studer 169 parametric eq pot: oscillation at max settings

Hello, I'm still working in my Studer 169, right now the psu is working fine, and every channel (minus one...) is passing signal correctly, my main problem is the parametric eq is oscillating when gain knob is at the maximum/or not so maximum position.

As I understand  in this filter design, the opamp is working with in phase and out of phase signal in the wipers of the potentiometer, in a differential way, and when they are not exactly matched in resistance the oscillation appears in the signal path. Main concern here, is that is really difficult and really expensive to find those potentiometers, do you think that cleaning or other surgery could save pots? Or there is any other way for compensating the difference in resistance?

Thanks in advance...still going step by step with this little console.

Something good happened... :-X at least for me, after having the console turned on during 7 hours, there is no oscillation on any eq.

Sometimes is just question of time?temperature?