Re-Sealing Tank

Being totally frank, this is how I see it:
The expensive silicone is not necessary and it's not that expensive, maybe $50/tube, but I would definitely suggest it for that size of tank.
Is there a frame or no frame? Clear or black silicone?
Used tanks are risky business. It's usually impossible to tell how old the tank is. Silicone ages and loses cohesiveness, especially when the tank is empty and left out in the sun or the cold. It's difficult to know what kind of abuse the tank has gone through. That's why used tanks, even only a year old are worth less than half retail price.
Another leak could happen at any time.
A second leak in another place indicates the need to reseal the entire tank, at least all the way around the inside bottom and 2-4 inches up the inside corners. The expensive silicone will ensure it doesn't come apart at least for a year or two.
Was this person you paid, experienced at this? If they were they should have suggested this complete reseal right from the start.
This may not be what you were hoping to hear, but you deserve to know the truth.

What type of stand do you have it on? Is there any gaps at all where the black plastic trim meets the stand? Is your stand dead level? FIY good silicone is not even close to $80 a tube. You want Momentive RTV 100 series silicone available at Grainger. This is a structural silicone adhesive and is VERY strong.

Frame or no frame?
That will make a difference.
I use a single piece of Malamine board. It's very strong and holds it's flatness plus it's water resistant.

If your interested, I build glass tanks and can take the bottom panel off and redo the whole seam if you want. I have done this many times, looks like factory when its done. This would be much cheaper then a new tank.