How Common is this? Original capacitors are still within spec.

Hi everyone. I’ve acquired some JBL l-166A’s and have been going through them to see what components if any needed to be upgraded or replaced. Last night my father who has an electronics background stopped by to check the capacitors. Visually the look fantastic and when a reading was taken using his capacitance meter the came well within spec. Curious how often this happens? Mind you this is without the speaker being under any load but it seems like a good indicator of the overall health of the capacitors even after 40 years. After measuring, I’m now thinking I’ll continue to run stock caps until my ears tell me otherwise. What do you think?

Below are some pics of the readings being taken.

Attachment 89308

Attachment 89309

Not all capacitors fail! Good thing, because a lot of the stuff from the 70's, 60's and even 50's would be going to the dumpster.

I repair old ham radios from the 80s and 70s (just after the tube era) and sometimes you can find a failed capacitor or two, but it's among the hundreds of them in a single radio, the rest of them are OK.

It all depends of usage, environment and well... bad luck. :)

Some caps measure fine capacitance wise but fail "exceptional series resistance" ESR measurement.

Ron sends...