MK 136 low volume output on the right channel only

1st question) Hey wondering if someone could tell me where to start looking for the reason of a low audio output on the right channel only. Approximately 1/2 the volume of the left.

2nd) Regarding the R8 and R7 resistors, which one is the right channel and which one is the left?


R8 is connector to the tip of the 3.5mm stereo jack, so this is the left channel.
Volume difference is most likely caused by soldering/assembly problem or wrong resistor value, please check.