Well, good luck with your other models when you work on them. They're probably too old to find someone who'll sell OEM cosmetic replacements for the destroyed discs. Maybe your instrument owners won't mind the naked handle securing fasteners, but I'd check a few vendors to see if you can find discs/caps that you can replace the destroyed ones with. If your workplace is anything like mine, the only reason whomever is USING this instrument has not gotten inside of it and tweaked any values they didn't like, was that they couldn't figure-out how to get the cover off. Those exposed handle fastening screws are going to be a tempting target for anybody who thinks they can just
get inside of the instrument and adjust potentiometers. Some people have just enough knowledge of things like this to be dangerous.
Hope to hear more from you here in the future. The more people we have on this forum to ask questions and offer advice with things like this, help everybody.