The wind tunnel in Untertürkheim – an installation with history - Daimler Global Media Site
There is a w126 in this gallery in a wind tunnel, I'm not sure if this is the long wheelbase model like mine and I'm not really sure these views even assist me?
I found somewhere a photo of another w126 being tuft tested. It may have been in a wind tunnel as well. The chassis seemed to have good flow attachment characteristics.
I'm sure there has to be room to improve on 42 year old designs.