Hi Reef Swimmer,
I can't quite say I successfully resealed a large tank yet as I haven't put it to use yet but it passed the leak test with flying colors so I have good hope that it is going to work. If not, then I have good hope that my laminate floor will look better as a tiled floor.
Check out my build thread for what I did.
http://www.austinreefclub.com/topic/29288-jeepertys-215-gallon-sps-tank/
Off the recommendation of OffRoadDodge, I used Dow Corning 732 clear silicone. I just ordered it online. Took me about 2 tubes of silicone to do the reseal of the front glass but in my defense, the glass was 3/4" thick!
I didn't go into too much detail on the build thread on what I did to prep the glass and remove the silicone so I will elaborate more here. My tank was only leaking on the front left side so I decided to remove the whole front pane of glass after an internal seal fix didn't do the job. If possible, I would try the internal seal replacement first and see if that works. You do that by cutting the internal seal from the corners/edges of the tank, leaving the silicone sandwiched between the glass alone. You are only removing the internal seal, not the joint seal. Here's a good guide I just found.
http://www.aquarticles.com/articles/management/Spinelli_Resealing_Aquarium.html
Quick note, don't use the silicone remover near any silicone that you are aiming to keep. It may help loosen the bonds and that's not good if you want that silicone to keep holding the glass it's been holding up to this point.
If that internal reseal doesn't work, then I can run you through how to remove the pane of glass that is leaking and do a full reseal on that pane. Good luck and let us know how it goes!
-Ty