I've found the CAIG chemical products are the best for this. You can use one or two of their sprays. For the super dirty pots, start with a quick blast or two of the MCL 5% aerosol spray and work the pot around its full range a bunch of times. I'd let it sit for a while...anywhere from a few minutes to a few days. Work it around again. Then hit it with a quick blast or two of their D5 5& aerosol and work it around as before. The MCL performs the majority of the cleaning and the D5 cleans and restores lubrication. You may be able to get by on using just the D5.
(If you don't know where to spay, there should be a notch in the pot just under the solder lugs where you can stick the spray tube).
A word of caution...be sparing with that stuff. A lot comes out with just one spray. It's safer to spray a little bit and re-test the scratchiness of the pot rather than spray too much and risk ruining it or its rotational tactile feel.
BTW, I really like the DeoxIT D100 liquid. It works wonders on jacks, plugs, tube pins, etc. I use it on everything. In fact, just tonight I just cleaned a scratchy input jack on my F*nder Deluxe 85 (which had been sitting in someone's garage for over a year) and it works better than new.
Don't mean to sound like a pitch-man here...I just like their products. You can get 'em at Parts Express among other places. I think the spray cans are about $7-8 bucks a piece. TechSpray also probably makes a good cleaner for pots. WHATEVER YOU DO, DON'T spray WD-40 in the pot! It may work for a little while but you'll probably RUIN the pot! Be wary of Radio Shack cleaners as well.
Good luck!
