Hi everybody,
Two years ago I had the same problem in Italy. I was lucky to find the nut - which is a very special one, with what looked some rubber mounting - on the place I lost it. I tried to fit it for many hours but I could not do it, because there is very very little space for holding the nut and in my case the tread on the nut seemed to be damaged..I arranged an Italian mecanic and it took him and an employee more then two hours to fix it. I paid them € 100,- .
So it might be a problem that happens more often then we think. Maybe it is wise to use locktight when tightening.
Best regards,
Peter