My screen cracked overnight while it was parked in the garage, and when I disassembled it I found it was the top mounting screw that had just touched the edge of the screen causing a very small sliver of glass to flake off, which seems to have caused a weakness at that point - which led to the crack.
So, just check the lengths of all the mounting screws - especially if you've fitted any wind wings that require slightly longer mounting screws which might foul the screen.
I managed to replace the glass element in the original screen frame, but I shortened all the mounting screws by two or three millimetres before re-assembly just to make sure it doesn't happen again.

Sid

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