PrimaLuna Prem Preamp. tubes on left channel running 20* hotter than right.

Checking my 3 month old PrimaLuna Premium Preamp with my heat gun reveals that the three 12au7's on the left (looking from front) are running around 20 degrees warmer than the right side. Aprox 135* on left compared to 115* on right. I have changed out three different sets of rectifier tubes, and 3 sets of (6) 12au7 tubes. It makes no difference.  I would expect them to run even, indicating same current draw and voltage. Has anyone else run into this?
Thanks