I had my 100 gal split on one seam about 5 months after getting it. Now it is a custom made tank (aka not professionaly made) and I did buy it used, so not sure how old it is was when I got it, but nonetheless it happend.
Woke up in the middle of the night to the sound of water "gurgling" and splashing, which is odd because my sumpless tank is dead quiet.
Walked into the front room where the tank is to discover about 30 gallons of water all over my hardwood floors!!!
Tank had split on one corner from the top to about 1/3 of the way down, allowing approx 1/3 of the tank water to trickle out. (100 gal tank!!)
Did a late night cleanup, drained the tank down to 1/2 full (below the split) and re-siliconed it the next day. Let it cure for 24 hours before filling the tank back up. Thankfully I didn't lose any livestock during the ordeal, and it hasn't been a problem since (1 1/2 years later).
I do worry about it still sometimes, and definitely will feel better when I replace it with a new tank.