Taking a chance on stating the obvious, one of the more critical functions of a capacitor in an audio circuit is to assure the DC bias voltage of one stage of an amplifier does not enter the AC audio signal at the next stag. If your capacitor is leaking, there is a potential DC will enter the audio signal and damage your speakers. I recommend you have your amp recapped since you do not know when the cap will fail to the point of DC leak. DC leakage can manifest itself in sounding like humming, buzzing, crackling or general distortion. Another function is high frequency noise filtering. Replacing your capacitors will generally improve SQ across the board. Capacitor life is hard to predict and based on capacitor design, amp design, the impedance loading, and the amount and type of usage (how hard your speaker load is and how hard you drive your speakers). Class A designs that generate heat with electrolytic capacitors are most prone to short life. When I was an 1997 vintage Krell enthusiast, I used to recap every 5 years. Maybe that is excessive, but the process assured reliability of the rest of the electronics in my mind since my Apogee speakers produced a difficult load demand and I drove them hard for long time periods.
