My home stereo speakers are sometimes fuzzy and can be fixed by twisting the speaker balance knob back and forth quickly a few times. I think the contacts need cleaning (does this sound logical?). If so, is this difficult to do? How should this be done (it doesn't seem as though it should be too complicated). Can WD 40 be used, or should I shell out $10 or so for Radio Shack's little can of contact cleaner?

Find a contact cleaner and lubercant. Hardware store and even the big box stores should have it.

You do need to make sure that the control has a port to be able to spray the cleaner. Some are sealed and replacement is the only option.

I liked Channel Masters "Tuner Cleaner" Leaves no residue, and safe on plastics. They probably still have it, If it can't be done through the front, you may have to remove cover and spray control directly.
If Radio Shack is convient, it should be OK.

Radio Shack's current contact cleaner contains mineral oil. According to some things I've read on-line, in the old days it didn't contain this, and the cleaner with mineral oil seems to get mixed reviews. Is mineral oil OK for an Onkyo tuner/amp from the late 80's?

Thanks.

I don't know the effects on plastics, If you can just spray the control, you will eleminate problems. Have the stereo off and unplugged, spray and sweep controls from one extreme to the other several times.