Vintage Synth Repair

thanks for sticking with it, tom, & for returning to tell us what happened. is the korg yours or is this for a client? I think, in the fullness of time, I'd've been inclined to swap out that one chip. this sounds like an output impedance thing, as someone else suggested.
if the other end of the wire is not attached explicitly to something, then you may find you have drifting pitch again with changes in humidity.... just a thought.

me, I'd've brought it out onto an insulated metal plate on the panel somewhere & make it a performance controller.... :-)

duncan.