Just cut the old silicone out and clean it really well with alcohol. To keep it nice and clean tape 1/8" away from each seam with masking tape, put the bead down, spread it with your finger, and then pull the tape off. You'll never know it was resealed if you do it that way.
You don't have to rip the tank apart, just make sure the glass on each side of the joint is very very clean.