There's a simple component that frequently gets flaky on
a certain kind of synthesizer I use. The component is
called a "data encoder." Its something attached to a knob
that you turn to scroll through lists. It looks like a
pot, but it's not a pot. It has three leads, which I'll
call left, middle, and right. As you turn the knob, the
middle lead connects to the left lead, then disconnects,
then connects to the right lead, then disconnects, and
so on.

The connections have a rhythm:
.... Left (short pause) Right (long pause) Left (short pause) ...
Thus, the device knows which way the knob is turning and
how fast.

This kind of component quite frequently becomes flaky,
in that scrolling is erratic, sometimes making big jumps,
or moving in the wrong direction, or getting stuck without
moving either way. I think this happens because the connections
are not always being made on the left or the right or either
side, so the synthesizer gets confused about which way and
how fast the knob is turning.

I can buy replacements for these things, but they're not that
cheap, and replacing them involves a fair bit of work, opening
the synth, desoldering 5 or 9 joins, and soldering in the
replacement.

Now, it turns out that I can get easy access to these data
encoders without even opening the synths. Furthermore, I can
open them up to get at their innards without any trouble.
There's a top part with a disk attached to the post for the
knob that turns with the knob. It has copper strips going
out radially from the center like spokes. On the bottom, it
has three copper brushes which are connected to the left,
middle, and right leads. As the disk turns, its copper strips
alternately make connections between the brushes in the
way described above. The whole inside is full of some kind
of grease.

It seems to me that it shouldn't be hard to fix these things.
Perhaps I just need to clean the brushes and copper strips so
they make better contact, then replace the grease.

Questions:
1. Do people here agree it's probably simply a problem with
leads needing to be cleaned?
2. What's the best way to clean the brushes and strips?
3. What kind of grease do I put in such a component?