Recapping your amp

Aluminum electrolytics can even go bad(via dielectric polarization), given enough time, on the shelf and unused(http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.823.6133&rep=rep1&type=pdf). Of course, heat and cycling, also take their tolls, but- if your component is older than 20 years, it’s virtually certain, the caps are due for replacement, even if(to the eye) they seem perfect.   Ears adjust to losses in fidelity, when that loss takes place over time and most won’t notice, like they would, were the change sudden.(http://www.elna.co.jp/en/capacitor/alumi/trust/) (https://www.illinoiscapacitor.com/pdf/Papers/Life%20expectancy%20of%20Aluminum%20electrolytic%20capa...) (http://www.powerguru.org/electrolytic-capacitor-lifetime-estimation/)

A timing belt won’t degrade your engine’s performance, before it fails(completely). The point of my references was, that(electrolytic) capacitors do. Of course: to many, "...still working...", is good enough. Do you replace your racing tires, AFTER they blow out, or- as soon as they begin to lose traction?  One's course of action, will depend on how much they value performance(different strokes...).