[Kos-Mos]

It works really good. The main reason for water is that it will take the crap away (with the armature spinning, the motor acts as a pump). And it keeps everything cold and lubricated, so a smoother finish is achieved (wet-sanding a fresh paint job anyone?).
The water needs to be conductive a little for the cleaning to work (it will help the motor turn properly if there is carbon buildup on the com).

You need a glass container (empty jam container works great).
99% isopropyl alcohol
Brake cleaner can
Duster (with the trigger)
Ultra light silicon oil (AI GBBR oil or high grade RC bearing oil. I use Trinity Royal Oil)
A rag to take out excess water

And TAP water (does not work great in distilled water... tried it).

Put longer wires/clips on the motor and put it in the container. Ideally, you want the glass to be twice the length of the motor.
Pour water up to 3/4 (about 1" over the motor).
Add a little alcohol (maybe 1/2oz.).
Run the motor IN REVERSE on 3.0v for about 2 minutes.
The change polarity and run FORWARD for 3 minutes.

Take the motor out of the water.
Fully soak the motor with brake cleaner (to replace water).
Then spray with duster to remove the excess brake cleaner solution.
Oil both bearings with silicon oil. Place a few drops on the bearing, then turn the motor by hand to let it seep in the bearing.
You will need to re-lube the bearings once in a while (maybe once a year) since it is oil and not grease.

Alternatively, you can buy a com cleaner from Parma (made for 1/24 slot cars) and replacement brushes (again, for 1/24 slots). Take the hardest "speed" brushes you can find (as you want longevity over torque... theses are made to be replaced every week).