I recently read (on an audio problem forum, I think) not to use contact cleaner on faders. Generally speaking, I’d go along with that, or at least say ‘If it works, don’t fix it’.
One of the reasons that the advice was given on the forum, was that contact cleaner attracts dust. It doesn’t, but it can help it to collect. And also there are different contact cleaners. Some have more or less oil in than others. Servisol 10 has a light oil in it, which is not sticky and provides a slight lubrication against carbon track wear. Something like pure acetone or a petroleum-based fluid, cleans very well, but isn’t much help for the track wiper on a pot or fader to get it to slide easily without wearing the track. At the other end of the scale WD40-type stuff is a bad idea on any electronic equipment (it’s great stuff on high current gear of the sort you find in auto stuff) that does go very sticky after the suspension fluid has evaporated.
If you’ve ever squirted contact cleaner into a fader you’ll know it feels like sliding over grit afterwards. This is because the slot in the metal chassis of the fader has a light grease applied to it during manufacture, and a sprung plastic sledge device runs on the inside of this. This grease has no physical contact with the electrical part of the carbon track. But spraying the fader will usually clean the grease off, and your fader becomes the gritty component we’ve described.
The technique for servicing a fader: first, just try whacking it up and down the full length of its travel a few times. They tend to be used in same positions, often; so they wear in a particular spot, and also collect dirt there. If that doesn’t do it:- get your servisol 10 spray with the plastic nozzle, and poke the nozzle right down to the track as far as it will go. Then just twitch the button on the can to let the tiniest drop of fluid out. Do it in three places, top middle bottom of the track. Then whack it up and down. If it feels bad, you used too much, or got a drop on the greased slide on the chassis.
If that happens, you get a very small, flat blade screwdriver with a drop of light grease on the end, just dip it into the fader slightlyand pull it out again, sliding the blade against the slot in the middle and leaving a tiny blob of grease under the slider. Then slide the fader slowly up and down (gently; you don’t want to splat grease onto the track). That should feel like new again, but if not, repeat the process.
If your fader is suffering wear, then this is not a cure. The cure is put a new one in. But plenty of faders sound really bad and its only dirt. So the cleaning thing is worth a go, as you don’t even have to take anything to bits.