How to maintain the sliders “clean”?
Use a Q-tip and very gently run it across the inside of the slider. If you are not careful you could damage the surface of the slider, be very careful. Some people use Fader/slider spray to clean them. Make sure it’s a fader/slider cleaner not all sprays work on potentiometers. If you are not sure ask a professional tech. WD40 is not a Potentiometer cleaner.