George,
If the windshield has the slightest twist when going over rough roads or into driveways it can crack. That is why when I put mine on the other Cobra I measured and measured to make sure that I had both arms on the sides at the exact same height when they were bolted onto the frame. My visors kept cracking from when I would be racing or driving hard and I think the vibration and stress just made those small screw holes through them keep cracking so I had a set made of Lexan and never had another problem. And I just cleaned them and the wind wings with water and a soft cloth and never had a problem with any scratches.
Ron