E320 Coupe (94) Emissions/Throttle housing

[Edcam]

I have a '94 E320 which I have owned and loved for c. 25 years which is now in need of some restoration. One of the issues causing MOT failure is emissions. Mercedes main-dealer not interested in the job. Gave it to an ex-senior technician of the main dealer who set up on his own a few years ago and was recommended to me by someone I trust. He identified the throttle housing to be causing the problem. He sourced and fitted a reconditioned one but it didn't solve the problem. Says he has been able to source another (in case the first was faulty) but the problem is that the polarity on the housing is the opposite of the car and he "doesn't feel confident enough in his knowledge of the electronics to re-work the wiring" and has now (politely) passed on the job. I have tried speaking to couple of other companies who I hoped might be able to help me but both have declined. One of them told me that I needed to have the original part number (which I no longer have) to be able to source the right replacement housing as "there are 7 or 8 versions" and without it the "car is scrap". The ex-main dealer technician that originally looked at it for me tells me that is incorrect and that all you need is the chassis number. Does anyone know of a reliable company that could look at this problem for me? I live in Cambridge area. Any help would be really appreciated. Thanks.