I think I'll need to take a closer look at any identifying numbers on the connectors when I get home.

I found at page 12 of this pdf on the Beru web site there two different parts for the connector - one for the bare thread [4 mm] and one for SAE style spark plug tops.

So the ZLE 121 [0 300 062 102] style would attach directly to the threads, and the ZLE 135 [0 300 152 106] style requires the SAE style knob on top of the plug. Probably the mechanic didn't notice the mismatch.

The number on the connecter is 0 356 321 028 - trying to find something online ....