Uh Oh! Silicone seam trouble

[Matyas]

Hello Everyone!
I recently purchased a used 75 gallon tank on my local forum and noticed it had one large air bubble in the seam. It is approximately 3 inches long and all the other seams look good. Is this a possible burst or leak? If so then how could I fix it?
The guy said the tank was 3-4 years old

 

[Diesel]

That’s big time trouble.
I would try to reverse the sale.
Fixing this results in taking the whole tank apart, just a seam won’t do enough.

 

[KrisReef]

I can't tell exactly what I am looking at in the pictures, but it kind of appears there may have been a seep there before, and someone already added silicon to stop the seep?

Fill the tank outside and see if it leaks, if it does, that panel would need to be resealed.

 

[ca1ore]

I'm not really sure from the pictures, they're mostly out of focus. Is the bubble in the seal inside the tank or in the structural silicone between the panels. If the latter 'danger will robinson'.