Gear unused for a long time (years) need reconditioning - applying lower voltage (perhaps 50%) and increasing it slowly over day or two. It is because without the voltage electrolyte eats dielectric layer (aluminum oxide) reducing breakdown voltage, while presence of the voltage rebuilds this layer.
Electrolytic caps simply dry-out over time. Each 10degC temp increase cuts life of capacitor by two. At room temperatures you should get at least 50 years. It might appear as poor control over bass (wooly bass) since dried out capacitors have higher internal resistance (ESR) thus reducing dynamics. When caps are really old and show symptoms of high ESR they should be replaced because they could explode. It is because higher ESR increases capacitor's temperature and temperature increases ESR - avalanche effect. You don't have to worry about it perhaps for 40 years (if we're still alive).
