make sure you get GE I windows and doors, GE II is harmful for fish cause it has the anti mold stuff in it.
GE I windows/doors is what ive used to reseal tanks,
i the last 3 months ive resealed, a 29, a 65, a 75 and a 125, none leak and all are currently in use, i put the silicone on much thicker than the factory did, and i have a wider seal, it takes approx 2 days to completely cure.
i used a long razor blade i purchased from a lowes (approx 4" long and 1/2" from sharp point to back) stripped ALL the old silicone off from the bottom and sides (left the top ring silicone alone and about 1/4" down from the top on the sides (not alot of pressure there anyway) used acetone to clean the glass and silicone residue off, the cleaner the glass is the better your seal will be, then put a bead of silicone around the bottom and up the side corners then used my finger to make a smooth U shape into the silicone, this also works the silicone into the corners of the glass, make sure you take your time and keep your head out of the glass, the fumes of the silicone will knock you out. or burn your nose.
dont run your finger backwards, once you have passed your finger over the silicone you dont want to go back to re-adjust it 5 minutes later, it will make it look worse.
*IF* you do all this and it still leaks, then you didnt clean the glass good enough, i spent most of my time cleaning the old silicone residue off the glass.
after 48 hours of the new silicone drying, i filled the tank to 25%, after 3-4 hours, i went to 50% and added 25% every 4-6 hours till full just to make sure there were no leaks, do this outside on a good straight surface, 90% of all tank leaks are traced back to non-level surfaces that create pressure in certain areas of the glass.
matthew