Looking through this thread, I'm thinking the posted results indicate that the failures are much more closely related to age than miles. To me, it makes sense that age and heat cycles would be more of a factor(s) than miles.
That photo above maximizes the appearance of the current "crack" that's developing. I wiped it down to remove the dust, and the light highlights the dust that is deposited in the crack/joint. For example, there is zero crack at the side joint, yet the dust makes it look like there is. I have other photos where you pretty much can't see any crack at the bottom joint. I'm going to keep an eye on it, probably replace it in another year or so, or sometime when I feel like it. Or, sometime sooner, after the wrecker tows me home after it blows.