Vintage Synth Repair

Hi everybody,

I'm trying to repair a Moog Source that has a few problems. So far I was able to fix the problems by reinstalling a new 5 volts regulator and doing a cleanup of the internal connectors. 

But the problem I'm having is that there is a few membrane switch that does not work.
The defective switches are located at the right of the synthsizer: OSC1, all of the switches of the Voltage Controlled Filter, all the S and R switches of the ADSR.
So far I've tried to swap the chips in the matrix circuit but that did not help. 
I guess the membrane itself is defective.

Is there any way to repair the membrane if only a group of switches are defective?
Thank you!

Nicolas