Sorry to hear about your need for pain killers Pal. My wife is just getting over a pinched nerve, so I know a bit about the effects of pain killers.
I seldom question João's answers, but in this case, based on your previous answer, I don't think our mystery coachbuilder is located in Berlin (as was Kellner) unless you are not counting the Western occupation zone as DDR.
I am not having much luck locating German coachbuilers who worked on British chassis (outside of Rolls-Royce) in the inter-war period, probably for obvious reasons. Somehow I think I see some French influence in this vehicle, so I will try a coachbuilder located a little closer to France. 1933 Vauxhall by Hebmüller?