I have a pair of MC402‘s that are probably the same vintage as your MC501s. I opened them up specifically to take a look at what McIntosh used for caps (there was a huge problem with inferior/defective caps 10-20 years ago
https://en.m.wikipedia.org/wiki/Capacitor_plague).
To McIntosh’s credit, they used high quality caps in most of their equipment and avoided a lot of the problems that other consumer electronics manufactures had.
You should be good to go for another 10 years without an issue.