Discussion about the Korg PolySix synthesizer

I've come across several P6 voice boards that have one oscillator 
(usually the first) that lags behind the others in coming into tune -- 
sometimes taking up to 20 minutes.
What is it in these oscillators that is temperature sensitive?  Or is 
this actually a temperature issue, or something else?
The board I'm currently working on has had all the caps and 
semiconductors on the first oscillator swapped out, and the oscillator 
will tune to the others after a 20 minute warmup;  but I'm curious as to 
why only one oscillator would behave this way.
Thanks.
~GMM