When is used used up?

All I can say Elizabeth, is you really seem to be in the know. Hats off to you! I learn something new here almost every day.

Liz, good thoughts on environmental factors. I did not include the question molecular decay of components and connections which is a factor of the quality of construction also. So, I guess we have -- where used, how much use, and what is it.

How's that analogy work for us humans?? Same/same I guess. I personally know I have been out in the sun,way long.

Players with motors can wear out, like turntables and CD players. Plus, CD players have lasers that, like light bulbs, eventually burn out and need replacement. Electrolytic caps in amplifiers can dry out, though modern ones are much better than in days of old. The key to these is if they have been kept in use so as retain their form; amps which have been stored a long time without use are more prone to cap problems than are those that have seen regular use so I always check on this point. Resistors can drift off value, zener diodes can crap out. Speakers are a mixed bunch; I've heard 40 year old speakers that sound fine, their cones and surrounds are still intact. I have also experienced a complete dust bowl blow out when a ten year old speaker was fired up that was working fine a day ago. Perhaps cables are more dependable components simply because they have the fewer "moving parts."