Now, restoring the pegs ... On one of my zithers with very old rusty pegs, I took them all out, cleaned them thoroughly with fine wire wool (be cautious, as you don't want to damage the shallow micro-threads, so always go WITH the thread, never against it) then completely degreased them, then bathed them in dilute vinegar and water so that they had a thin EVEN coat of rust everywhere, and then treated them with "Kurust" rust passivator, then varnished them to seal them. This is essentially the same as old-fashioned "blueing", used on vintage firearms, etc.