The guy that just got done calibrating my $15,000 signal generator said that the best cleaner / lubricant that he has ever used can be found at Radio Shack !!! This guy services and calibrates hospital gear, TV & FM broadcast stations, etc.. and has been doing so for 20+ years.
The solvent that he's referring to is their TV tuner cleaner / lubricant. Don't buy the "color" TV tuner / lubricant spray that costs more, as the only difference is that it is scented. He has used it in "sealed" controls over 12 years ago and it is still "liquid" and not all "gunked" up. Then again, ANY cleaner / lubricant will get nasty if you have it in an extremely dirty / dusty environment. I'm sure that someone makes this for Rat Shack, but we don't know what manufacturer or product name that it is directly marketed under.
My experience with this cleaner is that it worked well and i've never had a problem with it. Since i use a LOT of solvent at work, it was simply too expensive to use all the time. I prefer the Rat Shack stuff to the highly respected and widely used ( by technicians ) "Blue Shower" foaming cleaner / lubricant any day.
The stuff that Bob mentioned ( Electrowash ) is quite good for initially flushing controls out. However, if you do rotate the control quite a bit or it has metal to metal contacts that can pit, a bit of lubricant can be a good thing.
Here's a link to something that might help you or some others better understand how to clean a control or switch. At the time of this post, i had not used the Rat Shack stuff. Shortly after that, we ran out at work and i had to pick up some "emergency" supplies. The Rat Shack stuff worked MUCH better than expected and i wouldn't hesitate to recommend it. Just keep in mind that it IS lubricated and follow the guidelines that i mention in the post below. Sean