also, the middle/third brake light operates off only two wires - ground (pin 1 of the third light connector) and signal from LCM pin 10 off connector X38 coming to the second pin (pin 2) of the third brake light connector...

so, there is no separate signal from LCM to the left half, or right half of the LEDs - just one pair connection... therefore, it is safe to establish, that the internal board that houses the LEDs is damaged or fried... since the item is replaced as a single unit, i think it would be prudent to find one from a junk yard, and meantime try to repair the one that is defective... just an opinion...