In reality, nearly all components can or do degrade in performance rather than or before total failure. This is true of caps, resistors, ... and solidstate devices. When things are working and sounding good, we simply take them for granted. Unfortunately, it is only when things fail that we are educated as to the many possible failure modes of even relatively simple circuitry. A good repair facility/technician is a highly valued commodity in this crazy hobby. Be nice to them because you never know when you might them!