Needless to say we ran into some troubles fixing the clutch. First the gearbox was stuck, we needed 4 people and massive tools to remove it. Then it turned out that the release bearing was damaged because of a broken spring was is supposed to hold it in place. A 3 EUR part, but not in stock in Austria.
Now I am waiting for the spring to arrive, Nissan say it is expected tomorrow. Then we still have to install the 200kg gearbox (see below) again.