Roger,
You may have to, unsolder the leads from the diodes from the rear wafer, loosen the nuts on the rear of the switch enough to keep them on, loosen the nut for the pot, move the pot back enough to get access to the tabs holding the metal case on, pry the tabs back enough to get a gap where you can spray cleaner inside then reverse to get back to original. It is possible you will have to remove enough to get the pot out to clean it. I know it is a lot of work. Drilling a hole will get metal shavings inside the pot. I had two pots that were open in a Bogen DB130 I had to replace the guts. That had a similar thing as you have, a wafer and wires that needed to be removed. This has concentric controls. It took a few hours in my case. No other way was possible.
Mark
