I've seen a couple of basic x doors with a crack just rearward of the upper hinge. I think it is from being swung forward without the limit strap being in place.
I had thought that it would never happen to me, but after installing X doors onto a Humvee and using brand new limit straps. I had the door open and a big gust of wind pushed the door forward, snapped the limit strap and the door hit the lower hinge of the mirror. Luckily no crack, but it was a violent event! Learned my lesson right then. I had used limit straps for the soft doors. They have a stamped steel bracket which will cut the strap if stressed enough. The proper strap has the same bracket that has been dipped in some sort of rubbery black stuff to keep the strap from being cut.
