From the site of Horst in Germany.
Doorlock on front right does not hold the door when closing the door,door is always open.
Fault: a piece of a spring inside the doorlock is broken.
Repair without using a new part: the spring has enough length to unwind a piece and make it working again.
Detailed with pics, no need to understand German. Click on the left side in this link in the word 'Tuerschloss' and the file will come up, takes some time