Prima Luna Dialogue One Balance problem

My PL Dialogue One Integrated amp has a balance problem.

Left channel is less lively, sounds probably a couple decibels lower and highs are not as much present as on the right channel.

I have swapped tubes, tried new sets of spare tubes (driver and power tubes), swapped spk and ic cables and even speakers, tried different sources. I have PL EL34 and Genalec KT77 output quads and RCA NOS 5751 + RCA NOS 12AU7, as well as EH 12AX7 + EH 12AU7 driver pairs. The problem remains.

Any thoughts?

I see that there is a single trimmer potentiometer on the adaptive autobias circuit board. Should I try to adjust it as on the link here?

Does autobias alignment have an effect on imbalance?

Might just want to call Kevin Deal, it's his company
The Prima Lunas use the Alps Blue Velvet volume pot. IME, these pots always have a channel imbalance at low to moderate volumes. If you still have the issue at higher db, it's something else.