How exactly do old caps degrade the sound? Should this man re-cap anyway?

I just bought a CB Naim 160 with the original ITT '82 date-stamped reservoir capacitors. I was expecting it to sound pretty crappy and in obvious need of a re-cap, but amazingly it sounds great. No worse than my recently re-capped 250 (with 2010 Kendeils), slightly different in character but no worse. How exactly do old caps degrade the sound? Should I re-cap anyway? If so, which caps would you recommend?

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