To refresh the white lettering- get the knobs good and clean, get all the old lettering paint out of the engraving. Rub a very thin layer of Vaseline over the surface of the knob, being careful not to get it in the engraving. Spray paint the knobs and allow to dry, then wipe off the Vaseline.
For the lettering, purchase a Laquer Stick. It’s a soft crayon type product. You color in the engraving and then wipe the excess with a dry towel. Then wipe with a fine cloth, damp with laquer thinner to finish cleaning the face. Thread HERE
As far as cleaning the knobs goes, mine weren’t too bad, but i did add a CHOKE cable later which had a more worn knob. Simple green to get it clean and then polishing with a cloth and buffing compound brought it to a sheen that matched the other knobs.