Electrolytic caps are in danger to dry out after the years. It's mostly the case with power supply caps that carry high ripple currents, but can also happen to arbitrary exemplars. Elevated operation temperature are the most important factor in this regard. But how do you know, that the said capacitors are bad? In particular electromechanical switches and potentiometers are starting to show contact problems after decades, causing fading signal and scratching noise. Also various other parts made have lifetime limitations.
Systematic action would need a service manual and check specified bias currents and voltages, particularly of the power stage. Knowing the observed kind of quality reduction would allow an expert to presume some popular fault locations.
Using a higher voltage rating for capacitors is generally O.K., however.