What is the lifespan of a good SS Amp

I have a Harman Kardon int amp purchased in early seventies that's still operational. Pots and switches a little scratchy but if it's in the garage who cares? Had to replace an output transistor, actually one of those output packs they use on less expensive amps.

I have pair of Meridian active speakers that have astounded me for almost 30 years and the amps have never missed a beat let alone been serviced.
Maybe new caps would be an idea but then they might blow away my good system.
Si

There are too many variables. If properly ventilated, & not continually operated @ rated power, 20 to 30 yrs. isn`t beyond the pale.

Electrolytic caps (the big power supply caps are the primary ones) tend to dry out after 12 - 25 years. Higher operating temps usually result in quicker decline but there are differences among capacitor manufacturers too so it is difficult to generalize. Occasionally you'll see early failure or caps that last beyond 25 years but the above range covers "normal" situations. The electrolytic caps may loose storage capacity before total failure. Replacing these caps will usually cost $100 - $400. The rest of the components in SS amps are likely good for at least 50 years. The caveat is that some transistors are no longer available so if you have catastrophic failure you might be in trouble.

Well, if Bryston guarantees the many thousands of amps they have out in the world for 20 years, then you can probably use that number as a good baseline.