Usually most of these faders of all old vintage synth are quite dirty, usually they have never been opened until I get them on my bench. So I usually expect a lot of dust and dirt inside, so, again, it make no sense for me, just to spray in any kind of contact cleaner. This would temporarily make good contact, but you won´t get the dirt off the slider. You will also wash out all the junk which, when the contact cleaner dry out, spread all over the carbon track which makes it even worse. On my bench it's gets a proper, professional cleaning.