Wolfgang, I would like to ask you for some help as You live in Austria.
My wife's grandfather was Alois Plattner a Motorcycle racer who lived in Voraldberg, Bluedenz. He is also named a few times as from Thuringen.
I even have a website asking for info, but to no avail.
Is there any way that you would have some more info somewhere.
I post a picture of my KR RZ 500 with a Swiss young lady sitting on it in my hobby room.