I recently acquired a well-worn-but-working WM-D6C that sounds great - except the headphone output on the left channel is ever so slightly higher than the right channel. I've compared it with different headphones and different tapes, so I can narrow it down to the D6C.

In a traditional home cassette deck you can normally turn some potentiometers inside to adjust the playback level in both channels. Does such an adjustment exist inside the D6C?

Finally, while I'm asking - the unit's serial number is no longer visible. Is there any way from telling (without opening the unit) whether it has the newer PCB?