Discussion about the Korg PolySix synthesizer

On my Trident MKII, the 7th oscillaor takes time to get in tune.
Actually, the first few minutes it rises up slowly, to a much higher 
tune than the general tuning, the slowly gets down and stays about half 
a note down from the genreal tuning.... I replaced all capacitors in 
the 7th oscillator section, but still no help.

One thing I noticed, is that on 4066 chip runs on voltages a little 
lower than the same ones placed on the other 7 oscillators.
About 10% less. I also replaced that particular IC but still no help.

What else can cause this kind of problem ?

Thanks !