HI all

I've got a problematic Diesel, I'm gonna cut straight to the chase. If any of you guys have any suggestions it would be great. The car will not start.... It spins over... Diagnostic is showing Crankshaft sensor fault however this was changed. It currently with a BMW specialist who has cover many tests and is saying that the ECU could be at fault however he cannot guarantee that it will cure the cars fault and even he is reluctant to say buy a new unit! This leads me to my question.... If I was to buy a second hand unit would the DME numbers have to match exactly? I've been told no! but would like some further advise as to what I should be looking for to ensur that the ecu that I buy is the correct unit.
I intend to buy one with the EWS and keys so not to cause any further issues.

Please advise if you can.

Thanks Lloyd