Hi Gareth, I visited a couple of "tow bar "experts but got no real help - generally comment was they hadn't seen an Audi towbar before. I don't believe the mechanism is significantly different to others but anyway. One did comment that dirt may be in the housing on the car. I spent almost 2.5 to 3 hours lying on my back beneath the rear of the car and discovered that despite the use of a plug to seal the housing when the tow bar isn't in use there was build up of rust around the neck of the housing which took some time to remove with emery paper, WD40 and a sharp screwdriver. the main shaft inside was fine and well greased. Once I had that done the tow bar fits perfectly every time. Lesson learnt! Get the feeling not a great design here.
Kind regards
Brian