Hello ! I would keep the healthy one aside undisturbed as to compare in probing voltages.

The arrow below on the vertical board is on a plastic void with the +12VACC path coming from the label7 towards components in the void under this new arrow. I carefully sawed off the plastic, opening its rear side to gain access to peek and probe that area, harms nothing.
That would be my next action, to see if there is corrosion in there. The position of the saw blade would be coming out of that photo parallel to the board and flush to the extended rear plastic to the right.. If unsure or need better explanation, I will.

 

This is of concern ---> ..."I have voltage at pin #7 and many of the surrounding (22, 21, etc) on the unhappy unit"...

+12V at Label7 pin is OK, but voltage can 'leak' to surrounding areas if there is corrosion, as corrosion chemicals can be conductive... Compare voltages on those same points with the 'happy' unit, both with +12VACC supplied; in same OFF condition.