I have very successful experience with several vintage tube receivers, mono amps, preamps, some 1958, others 1964. Complex tape recorders from the 80’s. TT from the 80’s.
One example: McIntosh mx110z tube tuner/preamp, 1964. bought on eBay, tubes all tested good on my tube tester, listened, loved it’s sound for 2 years as received,
Then, sent it to Audio Classics for overhaul. Best thing they did was replace all the old rca corroded jacks with new gold plated jacks!
They replaced several capacitors and resistors because ’at this age, many of the components had drifted in value’.
Oh yeah, they aligned the FM tuner.
Great, but could I hear the difference? Nope, sounded great before and after, but those corroded jacks were problematic, new ones let me sleep better!
IOW, drifting out of value more than likely true, but audible, that’s hard to say.
Cleaning pots, switches, tightening tube sockets contacts with tube pins, testing tubes: I do that myself, but if not, the old stuff definitely benefits from having a shop do that.