The mechanic charged us 35 euros and had it all fixed. I think he was able to install it on what is left of the thread. It works just as fine as before.

I believe he was showing off when we first saw him. Competent craftsmen always show off. Before we took the bike away he wanted to see it folded and measured it folded and unfolded. He had never seen one of these KHS folding tandems and he was impressed obviously.