I really hope this is a rare occurrence (I think the few of us on Airforums with the problem are the only ones), but even if this is a common problem, I'd still want the rock guards. Rocks do fly, and I'd hate to see one go through a window. We have a rock "star" on our center window guard (which we didn't replace)...that rock guard saved the window. They are expensive though. The sticker was still on our guards when they arrived...$947 for the full set.
We will also follow Stingray's advice about not washing in the heat. The striations do look like plastic that has crazing marks from a dishwasher. However, we've had a really cool summer, and we're not sure we ever washed it in the heat. Though, we might have last summer and just didn't notice the striations until this year. The road side rockguard got so bad that we had to tape it from the inside because little chunks were falling out.
Lisa and Paul
2008 23' Int. CCD "The Atomic Pod"
1973 13' Boler (fiberglass egg) "The Boiler" (bolerama.org)
WBCCI #23223 (=23 CCD)
TAC- SK 23223