if you've not already, you could try switch cleaner and checking around the pot for dry solder joints. I've just resurrected a 32 year old Sequential MAX where the volume was all erratic and noise would appear randomly. Working some switch cleaner in for a while fully fixed it, like new now. No new pot needed. Also fixed the rotary encoder on a JD-990 in the same way, even though it was completely dead and I thought it was a goner.