Measure the DC voltage (if any) between the individual heat-sinks; while operating, but open, with additional external desktop fan providing additional cooling.
I'll try to accommodate this. Unit wasn't friendly with me when I had the fans disconnected or even connected, will try a workaround.
You can probe just a few random heat sinks while
all boards are normally mounted in the frame. If it
is anything else but 0V, we can run some calculations.