A customer sent us a video showing him pulling off an Avant that he just tried to mount to his GS_LC. While watching the video a few times, I saw that one of the clamps was properly aligned with the positioning ribs molded into the inside of the Avant, and one was askew resting on top one of the ribs instead of in between the two.
The Avant could not be affixed because the clamp that was twisted onto one of the ribs could not be drawn down with the screw to grip the fender. Instead, it was drawn down against a rib with the screw, preventing full travel. The attached photo shows a clear pictorial explanation of correct and incorrect clamp positions.
Installation of the bracket is a somewhat blind procedure. After slipping the extension over the fender, one has to position a clamp behind the mounting flange and feel that it is parallel with the molded guide ribs with the forefinger when starting to thread the screw from the outside. Hold the clamp in position while the screw draws it down to the inside surface of the fender and grips it withits claw. Repeat on the other side. Then, go back and check the tightness of both sides.