I would like to add a few comments, based on some of the replies in this thread. Getting "most" of the old silicone off isn't good enough. It as to ALL be removed. When you are sure you have gotten all of it, grab a new blade and go over it again.
There are lots of safe silicones out there including GE Silicone I for "windows and doors". Do not use any silicone that says "Tub and Tile" or "Kitchen and Bath" . This has been stated many times but bears repeating as people are still making that mistake. I generally use a house brand that states "aquarium safe" on the label.
Cleaning the seam after old silicone removal and before adding new, with alcohol or acetone is important to remove any oily residues such as skin oils from the seam area. Neither alcohol or acetone will remove any silicone residue left behind after the scraping operation.
Cure time is relative to the size/thickness of the bead applied. A really large bead is counter productive as it is difficult to get a clean, feathered edge if the bead is too big. Regardless, the house brand silicones have a cure time for a relative thickness, but add a day or two when used for aquariums.
When testing a resealed tank, it is often recommended it be done outside. This is fine as long as the same care is taken to place the tank as you would for setup. It needs to be on a sturdy, flat, level surface to avoid any torquing that could cause the tank to leak or even fracture. Don't ruin your efforts by taking a short cut here.
A lot of people are afraid of tanks that have been resealed, but at least half of my tanks are reseals that were bought as leakers after they were returned to the store.
If the crack is on the bottom and its the frame I'd be weary of using it too. It's really hard to gauge though without seeing it. If you're anything like me, I'd use it as an excuse to get the 125 
