too much distortion!!

the other day i was listening to music and when a quiet passage came along. i noticed some harmonic distortion from both channels. so i unplugged the source rca. then turned up the volume knob on the sansui. it sounded like harmonic distorion. (from low freqs. to high)it was quite loud sounded like in the 10 percent harmonic distortion.
now this reciever is about 35 yrs old. would the output caps be getting dried out?

i think these are what they are.

there are 3 of these:

ELNA
CEW
80v
2200uf
black -neg.
35-F

another one with the same writing but it is only 1000uf

these are screwed on to the board. with a clamp holding the capacitors or is it transistors.
besides the point they seem easy to replace as they are connected by wire soldered to terminals on the caps. but ive never done anything like this before. though ive used a soldering iron before.

any one come up with any ideas as to what could cause the distortion. or a website that could clue me in?

if the parts above could be purchased ...if so from where?:( the reciever is still playable. just that when turned up then during quiet passages i can hear the distortion. it is speced from the factory with much lower distortion then what im hearing.