If you do a proper job resealing a tank it is a lot of work. Expect to spend several hours cleaning the tank and getting it ready to reseal. You'll go through several razor blades to get the majority off. Then it is wise to use acetone to clean the glass. It needs to be spotless or you run the risk of a bad seal. I would use a high quality silicone, something better than GE I which is a sealant, not an adhesive. RTV 108 is your best bet, you can get it through Grainger. Silicone will skin over in 3 to 5 minutes, depending on humidity in the room. If it skins over you have been too slow and will need to start over. You want about a small bead of silicone, up to about an 1/8th of an inch at most. Use clamps to hold the tank together to dry, not tape or straps. Give it two weeks to fully cure, while the outside may seem dry before that silicone dries from the outside in and wont have full strength until it is all fully dry.
That all said, I have to think it would be easier and not much more expensive to just buy a new tank. I get wanting to DIY but for such a small tank I'd rather have the piece of mind knowing it was done correctly and not need to worry about 40 gals of water on my floor.