[Jonny042]

I have to admit I have zero familiarity with this circuit, but the pictures of the sensor I found online look the same as yours so I don't think you're missing a piece of the sensor. However, I did notice the sensor seemed to be listed for years 76-84, so maybe you have an incompatible sensor?

Also, passing a magnet past the coil of the pickup should create a small voltage pulse, not a change in resistance (I think). Again I am not familiar, so it's possible Porsche designed it to emit a square wave 12 volt output and you're on the right track.

Hope you can get it sorted soon - you really need to find a more agreeable mechanic!!