WD2500BPVT - Short circuit?

WD Internal Drives Desktop & Mobile Drives
7

Your measurements suggest that the short circuit is not at the +5V input to the drive. I can only imagine that it must be inside the motor controller chip, and that it manifests itself only when the controller attempts to spin the motor. In any case swapping U12 to a donor PCB sounds like your best option.

Best of luck.