Now you have me thinking too. I have been really wondering why the 200 - 400 would sustain damage when the others (24 - 70 and 70 - 200) did not. The one thing that could mitigate against the mount causing damage to the 200 - 400 was the fact that at no time was extra energy required to put the lens on the camera. If there had been a stiffness in the mounting process I would have suspected that there was trouble. Now I am also wondering if something had happened to the 200 - 400 that I was not aware of and this led to the Nikon Technician finding fault with the lens mount and suggesting repair was necessary. Inspection of the various lenses leads me to conclude that there is no difference in the construct of the lens mounts. They appear to be essentially interchangeable and there would seem to be no difference in the mounts. Consequently I cannot conclude that there are any inherent weaknesses in the various lenses which could lead to susceptibility to damage.