Amp showing its age?

Transistors don’t age. They keep working, staying within spec, and one day, fail without any warning. When that happens, as often as not, several other parts burn out as well (typically resistors). In other words, they work fine until they don’t.

The secret to long life for a transistor is keeping the transistor die cool. That’s a function of heat-sink design (more is better) and keeping the component well-ventilated.

The parts that do gradually degrade with time are electrolytic capacitors and paper-and-oil capacitors (not generally seen in modern equipment). Mylar and polypropylene caps basically last forever, along with adequately rated resistors.

So if you want your transistor gear to last forever, replace all the electrolytics every ten to twenty years, and get a small fan to keep it as cool as possible. Everything else should be fine.

Now if the circuit board design is really bad, with hot resistors next to capacitors, and poor quality solder joints, yes, it can fail in a few years, and can be very tedious to repair if all the parts are jammed together.

In your loudspeakers most likely the coupling capacitors ,I have been upgrading Xovers for years ,stock Xovers are in most cases average at best to save $$

upgrade-these capacitors and your speakers will sound better then before 

as long as the drivers are still in good shape.

The speaker caps are probably OK if the new amp is working fine with them.Speaker crossover caps will go bad, but not as quickly as amplifier caps, 30-40 years. If you were using  vintage speakers made from 1950s to 1970s, then replacing the crossover caps would make sense.

Years ago I read an article whose author stated  that as a rule of thumb,  capacitors on solid state power amplifiers should be replaced every decade or so.  This is even more pertinent when the amplifiers receive a lot of use. 👍

@lynn_olson  Mine is a case of gradual relaxation on driver grip, most noticeable in the bass. I was actually enjoying the bottom end end harmonic distortion, but when a notorious high amplitude signal in the low impedance frequency range threatened to blow the left speaker, I knew the time had come. Being impatient, and having no repair shops anywhere near, and also curious about the new iteration of Coda S5.5, I simply switched it in for the Parasound, quickly heard the difference, then posted this question.
@ audioman58, @chenry I'm not worried about the speakers, given that a new amp quickly removed their flabbiness. They are a little newer than the amp and now sound fully restored. So I now feel confident that their useful life without repair will exceed my own.