[Syonyk]

How much of that time has it been running?

I would wager that it's not been running powered on for 33 years without any repairs. If it has, probably long past due for a re-cap job, and you probably don't want to put a scope on the voltage rails to see what the ripple is.

For a broad handwave, "sitting powered off" isn't too bad for solid state equipment (it does bad things for hard drives, see "stiction"), but operating (and operating at temperature) is where the wear occurs from a range of effects. I've reworked [0] a Core 2 Duo board that stopped booting after a decade or so, because the capacitors filtering power for the IDE controller got so bad it wouldn't boot reliably (it would load the kernel off the drive, and then insist the drive wasn't present later).

[0]: https://www.sevarg.net/2018/04/15/on-art-of-repair-re-capaci...

[popotamonga]

Yes it ran 24/7 when i was a kid for about 4 years, nowadays i rarely turn it on.