Pots (potentiometers)and faders often become so scratchy and intermittant that they can render a piece of equipment unusable. This is usually caused by either or both dirt and wear.
Pots are made in both sealed and open types. The sealed types are usually well made and rarely get dirty but they can become scratchy from wear. They have to be opened to clean. Open type pots are easier to clean but are often of lower quality so they wear faster.
The Holy Grail of audio pots and faders is the conductive plastic and cermet elements. When pots are made of either of these two elements they can remain clean and usable for 10+ years. The well known Clarostat 388 and 389 pots use these good elements and are sealed as well. These pots are known to remain clean and usable for 15 to 30 years. But it's often hit and miss with pots, as there are open carbon based pots which last 10+ years.
Most pots can be restored. Like our switch cleaning process, we use a secret combination of safe chemicals to clean and re-lube pots and faders. In the case of sealed pots we can often open them to clean. With faders we usually disassemble the fader to some degree and clean both the element and the wiper. We also clean and lube the rails.