I found a Büssing 4000 T with similar bodywork in the Regenberg book. That was made by the Badische Fahrzeug- und Karosseriewerke from Weisweil. And I should have looked more closely before: this very Mercedes-Benz O 3500 Luxusbus is in that book, too.
![Smiley :)](https://www.autopuzzles.com/forum/Smileys/default/smiley.gif)