Bill was thinking very hard :
Is anyone here expert on these doors, or does anyone have a creative
solution?

As Google has demolished Picasa, the following is my first attempt at a
replacement to put pictures up. Hopefully it will work and make the question
a bit clearer (doubtful!)

I suspect some small nuts and bolts, or even pop rivets might do the
job, in clamping the loose end of the P to the rest. My guess is that
those metal P's will have to flex a lot, every time the door is opened
and closed, in which case they will eventually snap.

A better idea might be something like seat belt material, if the door's
weight can be relied upon to not need to be pushed down by the strap.

Mine uses 4x series of rigid nylon, curved, hinged straps, 5x sections
to each, rather like a course flat chain which fits closely to the
roller. I managed to damage 1 of the 4, so now it works fine with just
3 straps.

As the door is closed, at fully closed, the nylon sections go over
centre, so as to lock the door down in the closed position.