We once worked on a 1280 that apparently had liquids spilled on its faders (aka. slide potentiometer).
We have not found a good source for replacement faders with the same specs that will fit within the same footprint.
Therefore we usually clean these out.
It is really easy to spot dirty corroded faders when you look at them from the inside.
They usually look like this:
You can carefully take the backs off by bending the tabs on the metal body of the fader. Make sure to be very careful not to bend them too many times or break them.
We usually give them a good cleaning with a toothbrush and some Windex.
We extra careful around the contactors that are extremely fragile. If these fragile little metal whiskers break your fader will be scrap.
Here is a time-lapse from the last time I did this: