In article ,
Cursitor Doom wrote:

How it works: The threaded fitting has a small O-ring inside and is
threaded onto the switch or pot until it seals.

What thread are you talking about here? The one the shaft revolves inside
of that's used for securing the pot/switch to the front panel?? Can't see
how that would work. :-/

http://www.premierguitar.com/article...ning-miracle-1
mentions a somewhat similar device.

Consider the simple case - a hollow tube, with inside threads that
match those around the outside of the pot's bushing (the one you screw
the retaining nut onto). Screw this on, hold the pot with the tube
pointing upwards, and pour or spray a suitable cleaning solution into
the top of the tube. It flows down, and surrounds the pot's shaft
(which comes out through the bushing).

The shaft is not hermetically sealed to the bushing - it can't be.
There's always going to be a small gap between the outside of the
shaft, and the inside of the bushing... and the cleaning solution can
flow through this gap and into the inside of the pot.

For a "fully sealed" pot, this gap's going to be quite small - there
may be an O-ring seal inside, I suppose. So, you may need to
pressurize the cleaning solution to force it into the pot. That can
be done by forcing a piston of some sort into the tube, or by
attaching a syringe to the top of the tube (via a sealed cap) and
squirting/pressurizing that way, or etc.

A guy named Bill Turner used to sell an injection tool of that sort,
and also sold oleic acid (which can be diluted in naptha to create
something a bit like the original Cramolin Red contact cleaner). I
don't think he's still in business, though.