My early 20x SS (tasco) broke loose after 520rnds. The reticle rotated about 45deg and I could see glass shards in the tube, but it sure didn't crack the way this one did!
I did get some shot stringing just before it went out completely.
Here's a pic of the target I was shooting when it started to fail:
Tasco repaired it under warranty for 25.00 shipping/insurance.
After repair, it's still working great on a Serbu heavy barrel DTC gun.
It did give me enough time to save up for the Nightforce I'm running on my BMG now..
I tried a Leupold Mk3 on it too, but the eye relief was too short for my liking!