From what I see it is a hit and miss. I go to the junk yards a lot, and some cars never have the issue show up, and some the wires are just awful...

The whole car wiring does not go bad. Just the engine and mirror. A Mercedes document exist that test for a wiring harness issue..

Thinking of a W140, just get a 96 or later car, or ask about if the harness has been replaced.

Martin