I would take this approach. There's a possibility that they mean both volume knobs are analog, one sealed, one not sealed in which case contact cleaner would work fine on the non-sealed version. There's also a possibility that one is analog and one is a digital encoder. Spraying contact cleaner in a digital encoder might destroy it.

Please don't use WD40 on electronic circuits. It's a lubricant and will leave a residue behind. Any electronic store will carry contact cleaner. Or you can get it from that big mail delivery place that starts with an "A"