Hi Guys:
I do not feel confident enough or competent enough to try to pin down an exact date for this one (1926 or 1928) but here is what my research came up with so far.
I found four sites on the web dealing with this car. Three identified it as a 1928 model, one, a Russian site, identified it as a 1926 model. On a couple of the sites, there is a very brief discussion of Bussien/Voran working from 1926 to 1928 or 1929 on a 6x6 cross country vehicle together with Selve.
The car also appears in two books in my library dealing with the history of military vehicles. Both authors are well recognized authorities and I actually collaborated with both of them in the 1960's and 1970's. One author identified it as a 1928 model and the other discussed, in German which I do not read well, the same development story and was a bit ambiguous about the actual year of the photos of the car in his book.
These sites/books were in English, French, German and Russian languages and I have to rely on Google translate to try to piece together the story so I could be wrong, I could be right and I may never really know.
At least we know what it was, anyway.
BTW, I wonder if the M stands for Militär?
Bill