Maybe you can cut out along that screw line to create a gap for an expansion join, then silicon bead another length the same polycarbonate to create a lip for water run-off..

maybe a strip of roofing metal piece above that expansion gap to guard against splashing..

Plastics have huge expansion differences across their types so it might take a bit of trial and error but it could be cheaper/easier than a total replacement..

Just an idea..