I've resealed a lot of tanks in the past few years, and this is what
I've learned. Well, first of all, take EVERYTHING out of the tank....
put the fish in buckets with some form of aeration. You'll want to
completely empty the tank and strip out the old sealant with a sharp
razor blade or utility knife.... scrape it right down to the bare
glass. Then, clean ALL seams with a clean rag and generous amounts of
rubbing alcohol..... rubbing alcohol is the best thing to use because
it leaves no chemical residue that could come between the sealant and
the glass. DO NOT touch the seam after cleaning it.... even the oils
in human skin can ruin the bond of the glue. After the tank is
completely dried out, don some PVC gloves (wash them off thoroughly
with alcohol also). Use a caulking gun with a good, strong silicone to
reseal it (read all caution statements on the silicone tube to be sure
that it is appropriate for aquarium use). Smooth out the bead with a
popsicle stick or something like that. May wanna have good ventilation
in the room if you don't enjoy permanent nerve damage from the
silicone's fumes. Whatever it says for drying time on the silicone's
tube... you'll want to triple it before you consider putting anything
back in the tank. Good luck getting your tank fixed.