Aww, so it's basically old age? I'll try for a temporary cleaning and then retire them if it becomes objectionable. Thanks for the input.
Some of the current options use digital controllers instead of pots/faders. They can also be controlled via a computer interface (many wirelessly) so you can mount them anywhere.
I've run sound for an open mic night using one of the MIdas mixers and an iPad, it was a joy once I got the lay of the land.
EVERYTHING you could ever want is just a click or two away, EQ, compression, effects, etc.
Old mixers with pots need to be designed to be serviced, it's been my disappointing experience that lower line products like Mackie, the budget Yamaha line, and many others are "use then toss". Sad.