I had to take down my 55 gallon AGA over summer because the silicone was showing signs of failure (according to AGA who had looked at digital photos I sent it). It had only been set up since the previous November.
AGA was more than happy to swap out my tank BUT it was my LFS
that was a PITA because the tank wasn't physically leaking! Geez... let me go set it back up in my 3rd floor apartment and *wait* for it to break even though AGA said it was failing
I would investigate the break and what was sitting on top. Perhaps a heavy decoration fell (like stacked rocks) or it could have been faulty glass.