So guys, to bring that to an end - if there is an end........
I have dremeld apart this 250.- thing and found something that might be worth 25.- if manufactured in the West and even less if ...... you know what I mean.
Removing the 3rd brakelight is a 5 minutes thing if you look at the video in this thread posted by Brian - THANKS! 5 screws for the spoiler, 2 screws for the light itself.
If you have disassembled the brakelight you need to find the disconnection on the printed circuit. Solder a bridge over it (the white wire) and glue the whole thing together again with some silicone.
Done!
Costed 5 bucks and half an hour.
Have fun,
Helmuth