Uneven Control room output-still

[Tom Mix]

My determination (not my patience) is getting better. I lasted a full hour on hold for Digi support. That's way up from my usual 20 minute limit.
I'm back to trying to find a solution. The problem is obvious when I turn the control room knob to zero. The left side is still sending signal. A lot of signal. Sending pink noise set at 0.0db in protools. The left side registering 80db A weighted with the db meter 1 foot from the speaker. The right speaker is silent, as it should be, as I have the control room volume at 0. Yes, the test is mirrored when I reverse the cables at the C8 output. And using External Source inputs does not change anything.
Through my troubleshooting so far, I'm seeing that it must be the left output or the control room pot.
Any advice on this problem would be much appreciated. Should I open it up? Have any of you worked on the insides of a C8? My warranty is over anyway, but if anyone knows someone who works on these in the S.F. Bay area, maybe that's my best bet.

regards, TM