Solved: Wendax 1278 - Opel (?) Cabriolet by Schlesienwerk

[Wendax]

Yes, correct. To avoid misinterpretations, SS stood for Seehausen & Staar.

I think the base car could be an Opel.

I'll add the original picture tonight.

[Wendax]

Here it is. The picture was part of the postcard from August 1930. I can't decipher everything, but the writer talks about his new Cabriolet and a conversion of a van to a car, but I'm not sure whether that is a different car.