575SA wiper arm fault

Hi - My 575SA drivers side wiper blade arm rubs on the black bonnet lip at the bottom of its sweep. I had not noticed it until I saw the bright rub marks on the arm (only visible with the bonnet up). It is also wearing an indent in the black bonnet strip. I have dismantled and reassembled the connection between motor and arm but cannot see an easy fix. A new arm will not obviously fix the problem.

Has anyone else had this problem? You might even have it without even noticing? It must make a click sound on each return stroke of the wiper blade arm!