A leaking tank is a tank that's ready to fail. You'll need to drain it and reseal the seams before you can use it again. Sealing a seam isn't a difficult job but it does take some time and elbow grease.
Get everything out of the tank, drain it completely, and let it dry for a day. Pick up some razor blades, very fine steel wool, and acetone. Use the razor to cut and scrape away all the silicone from inside the tank, being very careful that you don't gouge the silicone that is holding the glass together between the panes. Once you've gotten out everything that you can feel, go over all the seams with steel wool and acetone. Remove any remaining silicone with the razorblade and repeat as necessary until you have an absolutely clean surface. Wipe down all the seams with a clean rag and acetone, mask your seams with painters tape, wipe down again, and apply fresh RTV. Smooth the RTV and pull your tape right away. I waited two weeks for the RTV to cure in my 180 but a week-10 days is probably sufficient. If you're doing this in a warm house you'll be OK. Cold garage=2 weeks.
For RTV, get down to Grainger and pick up some Momentive RTV103 (black) or 108 (clear). This is an industrial adhesive and is very easy to work with. There is approximately a 30 minute working time so you've got plenty of time to lay nice even beads and smooth it with your fingers for a pro look. I believe I remember paying $8-9 for a tube so it's not too expensive.
Good luck,
Mike