Hey Markus,
No worries....our caps will easily survive 20 + years.....it is not an issue with reliability, but more that of pure performance, and as I said before, there is an audible difference of a cap that has been used for 7-10 years vs. a new one...as for caps themselves, just like a tube, you can measure a cap to see if it is "good", but you really don't know if it is 100 %, 80% or 60% for example...it just measures good...but like a tube, you have diminished performance.....this is particularly drastic with oil filled caps (which we don't have)......it might not give you the same performance, but still measure and looks "good".....that's where the listening comes in. ... electronically, there shouldn't be a sonic difference then, but, again, just as in tubes, one can hear the differences.
having said that, it is particularly apparent in humid conditions, such as in Florida for example, as environs also play a role in this, and the process accelerates in PS caps when you constantly turn it on and off.
And then there are the Symphonic Line SL reference caps...expensive ? yes, but man oh man, they are fantastic, and they hold up big times with much, much less performance degradation over the long run....you definitely get what you pay for with these puppies.............
Finally, offboard caps in the amps are easy to exchange if anybody int'l wants to do that........and for all of my customers who want to upgrade or tune-up exchange any caps, we always offer them at close to cost anyway...