I had this happen on a corsa, it turned out the drive flange had cracked which mean that it was putting monster load onto the Nut, it was happily chewing straight through the split pin that retained the nut, just chopping it cleanly into 3 pieces and then carrying on undoing.

Not saying it will be a cracked flange on yours too, but something is causing rotational force to be transmitted into that nut more than it should.

Might just be the bearings are no good and allowing movement that way.


Is it the passenger side one by the way?