[codefox1]

There are thousands of opinions on the care and feeding of knobs. As always "it depends." Well wooden knobs can just about always be restored or replicated, bakelite requires remediation and wax, mold can be cured by a move to Arizona, common plastics can be buffed with a cotton wheel and pumice, etc, and metal knobs can of course be painted. Whatver, remove the set screws first, and replace them last if still good, or make new ones out of proper guage stainless steel. Yup, you can usually drill out and tap up to the next size most of the time.