I have been working cleaning the cap on a Martantz ST-7 Tuner. You could see on the scope the signal bouncing up and down as the dial is moved due to the intermittent contact made between the shaft and the ground wipers.
I have followed the listed procedure many times in the past and keep trying to refine it.
I think that a common issue is that many of the tuning caps were originally lubricated with a green conductive grease of some kind.
The DeoxIT breaks down some of the properties of the grease and then when the zero residue cleaner is used it dries out what is left of the grease, leaving loose tiny chunks. Depending on your eyesight you may not even be able to see them.
To get the rest of the crap off requires repeated use of the cleaning agents along with some mechanical removal. I have used a pipe cleaner very carefully to break some of the stuff free.
After initial D100, and zero residue cleaner 3 times:
This is a close up of one of the ground connections, not so good!
I carefully use a pipe cleaner, gently place it up against the shaft and rotate the knob a few times, breaking free all of the old dried up grease. Do not jam it in place, be gentle!
Crap on the end of the pipe cleaner:
After cleaning close up:
Once it's clean I use a pointed sponge type q-tip. This allows very precise application of the fader lube.
My concern with the lubricant is that it will not last. It would be great to know what the original lube was.