I have an Onix & Soap I purchased in 1987 and a Mac MC250 c. 1980 that work and sound perfectly fine.
I'm about in the same boat. My MMGs are fed by a B&K EX-442 Sonata w/Toshiba cans that is early 90s ('90 - '93, not sure which year). No issues whatsoever with sound or performance, but I've been preparing myself to ship it to John Hillig at Musical Concepts/Musical Design to have it refreshed with one of his B&K mods. Probably do it when I head down to Florida this winter, as I won't be needing it for a few months while gone.