Power amplifier longevity… thoughts?

Since I’ve bought a pair of Magnepan LRS+ speakers, I am searching for a used power amp with enough power and current to drive them as they deserve.

Some candidates come to mind and searching the used market (Hifi Shark) some are available for sale, for example:

- Classé CA-201

- Rotel RHB-10

- Acurus A200

- Muse 160

- Parasound HCA-1200 MkII

- Ayre V-1X
 

The possibility of buying a top quality amp at a friendly price is very appealing, especially comparing with todays new gear prices.

But the majority have way more the 20 years and one never knows the amp history, so there always the probability of a costly repair, and even the impossibility of restoration to the original specs when no parts or the service manual are available.

I wonder, in a general way, if an quality amp (and all parts) maintain the sound quality after all those years, needed only a check and bias adjustment.

Of course, in most hi-fi gear the capacitors and resistors are usually the first to need attention (change) but can those large caps (the size of a can of beer) last longer?