If you watch the action of the roll shutter you will see the edges of each slat is slightly rounded to allow 'roll'movement against one another. If they were square they would not move around the guiding slot. Have a look at the sides of the top section of guide slot some where fitted in section and were removable [I've seen one for the critics]. Just re-canvas it using Evostick but remember get it right it's a contact adhesive ones on you can't shift it.
Nobby
January 2009