Quote Originally Posted by akfotog View Post
As I said, I do trust the person I got them from, who kept all of his equipment in really great shape.
The deterioration issue is one of those laws-of-physics things. It has nothing to do with the owner, nor even with the storage conditions, only with time.

Reducing a rather complicated explanation to a couple of sentences...
The insulating layer inside a capacitor is made up of zillions of microscopic bubbles that form when voltage is initially applied at the factory.
These dissipate over time, but reform every time the capacitor is energized, within limits.
If the capacitor sits for a long time, so many of the bubbles are lost that it won't work reliably until new bubbles are created.
That's what happens when you energize the cap for a short time then let it sit, then repeat.

- Leigh