Discussion about the Korg PolySix synthesizer

After reading through some of all the messages posted here, I've realized that my problem 
might not be the opto-converter. PC-1. I might replace it anyway, If I just could get some 
instructions on how to do it.
But anyway, my problem with me polysix is this.

When i bought it it was in a slighty degenerate state, one occilator was out, and it was out 
of tune.
I managed to replace the IC on the occilator so that works, and now the main problems 
are:
1:
 i can't get it in tune. I managed to get 1,5 octaves in tune in the 8' setting, but as soon as 
a turn it to 16' or 4' it's out of whack. Especially in the extremes. So playing chords in the 
middle works fine (even if i play the same pitch in 16' or4') but i'd say the lower3:rd and 
the upper3:rd of the keyboard is way out of tune. An octave can differ up to an octave and 
a ters (third). Have I missed something. Or could this problem be the PC-1?

I've followed the tuning process in the service manual to the letter, but i can't quite get it 
in tune. All the trimpots have been checked as well. They all check out with the correct 
voltage.

2:
Sometimes when i've got the arpeggiator running and i fiddle around with the filters or the 
adsr the arpeggio tempo varies. quite a lot sometimes, it's almost stopping and then 
slowly gaining speed again. What could this be?

I have yet to bombard the pots with some contact-spray, but they are not to glitchy.

Any suggestions would be greatly welcomed.