Eldartford, WD-40 can dissolve some plastics (see the label), and can also dissolve the carbon resistive elements on some potentiometers, I've seen it personally. It's not as harsh as some other stuff that people try, and you might try it if you don't care too much about the given piece of gear, but definately NOT a safe general recommendation.
The "industry standard" for decades was Cramolin R-5, which is now sold as Caig D-5 DeOxit . . . the only difference is that the latter is HCFC-free. It works very well, but I recommend using the SMALLEST necessary dose, applied directly to the resistive element(s) and wipers. This usually means partial disassembly of the equipment, and spraying through the openings in the back of the potentiometer. The included little red straw is a must . . . you can even put a little bend in the end by heating it slightly, and blowing through it while bending.
I recommend using ONLY enough of the product to de-oxidize the contacts, and NOT to dissolve the lubricants used inside the potentiometer during manufacture. This means a tiny, tiny, little squirt! Or alternatively, DeOxit is available in a 100% solution in a squeeze-dropper bottle, where literally a single tiny drop is enough. The "flush, clean, and re-lubricate" process is usually only necessary in extreme cases (i.e. sliders on a mixer that lives in a smokey bar and has had a beer spilled on it).
