Solved: Wendax 1537 - M.M.C. 20 hp

[Wendax]

You got my hint. 
It is a M.M.C., but not the 10 hp. Locked for you to find the right model.

[4popoid]

MMC was going to be my next try before the hint, but the hint cinched it.  Assuming my estimate of 1903 is correct, this must be the one cylinder 8 HP (1021 cc).

[Wendax]

1903 is correct, but it isn't an 8 hp.

[4popoid]

Well, if my MMC reference is correct, the only other MMC model in 1903 was the four cylinder 20 HP (somewhere in the 1902-1904 model run it was uprated to 25 HP).

[Wendax]

That's what it is:

[4popoid]

Thanks Gerd.  Interesting that you should post the 12 HP as well.  I was afraid the 20 HP might be too large, and so went looking for other references.  I found a reference that says MMC showed a 12 HP at a January 1903 show, as well as the 6, 8, & 20 HP models.  I'm not sure why my first reference makes no mention of a 1903 12 HP model.