Denon Dra-300

[cathode_ray]

Have this antique with issues(can't find schematic). Headphones sound fine without speakers connected but when I connect speaker(s) left channel distorts on both speaker and headphones!
Ideas please?

 

[gni]

The output under load of the headphones doesn't draw too much
power. . .but with a real load. . .the caps don't have enough left
in them . . . .in any unit over 15 years old. . .start with the caps.