Not sure if it was looked into but if the chip was there and silicone applied over it by the manufacturer (making it a manufacturer defect), wouldn't the manufacturer be responsible for its repair under warranty or under an implied warranty of merchantability/fitness?
It's none of my business, but it sounds like from John, the tank manufacturer acknowledged that it was defective but felt it was still safe to use and offered it at a discount "as is". How else would it have been siliconed by the manufacturer with the chip and go unnoticed by someone? From a manufacturers standpoint, they would likely not waste the time to pull the tank apart, clean off the silicone, cut a new sheet of glass and reassemble it. The $ vs. time probably doesn't add up. In fact, I'd imagine we'd be shocked at how much glass gets tossed from chips, cracks, poor seals, etc. But perhaps in this case they felt it wasn't worthy of the landfill or recycle bin or whatever they do...
I could be totally wrong though and again, it's none of my business. I just offered my thoughts solely on the chip.