>>1795429>>1795436Found a solution: To repair this you need a new "Seegerring" or circlip and special pliers like in the pic.
I unscrewed the ball joint from the brake ever and put the new ring on. After screwing it back in just enough to fit back into the joint, I pulled the brake lever a bit. Now i could use the pliers to pull the ring together, put it into the cartridge and open it again. Now the ball joint/the washer is being stopped by the circlip.
My brake works again :)
>>1795430Went to my lbs and even they couldnt get it loose. now im buying a bike frame off ebay.