Help with purchasing an ML320 ECM

I looked around and found some used and/or rebuilt ones. I am now being told by Mercedes-Benz of OKC that I can't use one of those because they are ordered specifically from the dealer using my VIN number.
Is this true? I have heard of others doing this and was successful.
http://www.trademotion.com/partlocat...layCatalogid=0



