Almost certainly due to age, especially if stored in a damp place.
Kenwood KR-9600: leaking maxi electrolytics
I bought a Kenwood KR-9600 receiver last weekend. It powers up ok, but has crackling noise on the left channel. I pulled the bottom cover and the plate that's over the 4 power supply caps (80vdc, 10,000mfd). They all leaked, several badly. Of course, the ESR is way out there. There's no sign of overheating or other distress. Will it be enough to replace those caps or should I look for other problems?