Vintage Synth Repair

I've been in the process of refurbishing a polysix and have done due 
diligence with regard to the usual suspects (i.e. battery mod). The 
only problem that remains is pitch drift caused by what I assume to 
be a voltage leak in the LFO causing a subtle modulation  of the VCO. 
I have a working Polysix as well, and have had the luck of being able 
to A/B the KLM-367 boards between the two units. The problem follows 
the board under repair (I thought it might be the KLM-366 board). The 
unit is a "New Production" model. Any suggestions?