Yamaha CS80

talking about stability:
one of my CS80's took over one hour to get all oscillators pitched 
correctly while my other took only a few minutes.
So, I removed the old (and hardened)silicon-grease from the oscillator-
ic's and applied new grease and made sure the diodes were completely 
covered by it. Now, it takes 15 minutes instead of an hour. Why it 
takes still 15 minutes is mainly caused -I guess- by the fact that 
I've 1 or 2 ic's with different temperature-codes.
Now I only hope the new grease doens't eat up the housing of the ic...

About the codes, I think it's ok to use different -non matching- 
codes, but then you'll have to accept that during warming up the 
pitches are uneven.

Of coarse, tuning the pitches should be done best on a hot summerday 
or using a towel to keep the heat inside the synth...

Since, I'm not technical, can someone explain how the diode influences 
the pitch of the oscillator ?