I didn't read the links so this might be redundant but a standard diode test will be useless on a zener diode.

Since the OVP acts like a smart fuse, the easy way to evaluate it is to see if the devices powered by it are functioning. Not functioning right or wrong; just functioning. Just as a fuse can't make a system perform wrong, only not at all, the OVP either does or it doesn't. A standard voltage drop test is the absolute answer.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician