Generally speaking, it’s common for amp capacitors to eventually wear out and thus need replacement. At 20yrs plus it’s not surprising if your amp needs servicing.
Also, the sonic quality of SS amps has significantly improved over the years at various budget levels, and there’s a high rise in GanFet amps. So it’s may be better to change/upgrade than to refresh your amp.
+1 @hilde45 - make sure your room acoustics are sorted out

