Thank you for this picture, I didn't know him yet. But that is Kässbohrer and not Spermann. The shape is very similar to the Kässbhrer Bimot (I'll add a picture), but it lacks the maintenance flaps on the sides and there's one too many stars on the bonnet...My guess is Mercedes O/OP between 3500 and 6600. Judging by the tyre size, more likely 5000 or 6600, but that's a bit like reading in a crystal ball.