I built the K4040 amplifier and all seems to be good but there is one problem - the right channel sounds louder and bit noisy than the left side ???

Now I put the 8 ohm resistor (8ohm 5w 2j) between J21 and RED LS- and it works ! Is it dangerous or can I leave it ?

Best Regards

Normally, there is no need to add the resistor, it is ‘not done’.
Sorry, but the information you supply is kind of subjective.
Can you supply absolute figures regarding the difference in gain between left/right and regarding the S/N ratio?