I have gone over each and every connector on both attenuators, cleaned up the tin and carefully re-soldered all off them, along with the 4x lower lugs.
This has not resolved the problem, there is still a channel imbalance unless I turn the Coarse Dial to 0dB.
With coarse dial set to 0dB, I can use the source volume to go from quiet to loud, without any channel imbalance.. It sounds very good..
Fine dial does not seem to be affected.