My 99 got it's first crack around 200K miles. Now it is cracked all the way from windshield to front edge. Every time I hit a moderately sized bump I hear it crack more. My truck spent it's first 190K miles in the cooler temps of Washington State. I moved to Utah around 190K and then here to the really high temps of Vegas around 234K miles. I think hot summers make the plastic brittle and then the road bumps flex the brittle plastic till it fails.