MK1st,
I had this problem fairly soon after I got my PEK. The Deoxit (Radio Shack used to sell it) worked well for the PO8. I treat mine every year for the knobs that need it. For the PEK I have had somewhat less success. It was my oscillator shape knobs were especially screwy acting. So I applied the deoxit treatment an noticed some effect of success, but the "jumping" started to reoccur a few months later. It looks to me that the open port on the side of the little encoders is smaller on PEK and it's harder to get the fluid into the part. I eventually wrote to DSI who sent me two free encoders to replace my bad actors. It requires soldering, which I can do somewhat, but not extremely well. Anyway, I managed and while not pretty at all, I was able to replace that encoder.
Keep in mind in the meantime that you can just use the master soft knob by the display for any parameter you are currently adjusting (provided that isn't jumping too).