[Mark IV]

Chassis number? It is possible that you have a hub that is machined in way that prevents the axle from fully seating in the hub recess. The solution is minor machine work on the radius of the hub. A change by the axle supplier in the radius on the axle caused the issue, the factory was unaware of the concern until the cars got some miles on them and the problem occurred.

Let me know the chassis number and I can send you the factory prints that show what work is required.

When this issue is present no amount of torque on the axle nut will prevent the issue. If you jack up the rear and grab the tire at 12 and 6 can you wiggle it up and down?