I really like this shield is has an extended wing hanging over edges and a flat top but I am beginning to wonder if air on these wings have caused this?If you want to spend some time on it, I have had good luck with using a dremel tool in the hole but you must remove it and disassemble it to get at the shield itself. I used a diamond burr tip.
The dremel when used in the mounting hole to enlarge it just a tiny bit will actually melt it back together and stop the crack from spreading any further.
The crack is usually caused by the bolt that goes through the hole contacting the shield material where it passes through the brackets.