Capacitors can dry out over time, however can progressively age quicker due to heat. In Electrolytic capacitors the electrolyte is a liquid and can boil and expand under stress, either heat, drying or excessive voltage. The picture shows a raised top of this capacitor, due to the deforming of it the foil had shorted causing a short across the power supply. If this had not been discovered sooner it may have exploded, though not terminal would have created lots of white smoke. Regular servicing could identify this before it becomes close to irreparable damage. Book in your equipment now to avoid a potential failure!