Yeah if it's a seam that is leaking, then fixing it shouldn't be a big deal, and with a tank that big it'll be well worth repairing.
Keep in mind that if you have a leak on the bottom, that speaks for the condition of the entire tank, so resealing the whole thing is the best option. It's not all that difficult to do if the tank is empty.
Basically, you'll remove all of the old silicon from the inside corners of the tank. Once that's done, clean all of the edges with rubbing alcohol, use white masking tape to mask off the areas around the seams for good clean lines and just re-apply with silicon. Then, pull off the masking immediately after applying.
For more detailed information, google around. There are plenty of articles that outline this procedure complete with pictures.
The silicon you'll need is GE Silicon I Window and Door. If your tank uses black silicon, you can order it from aquatic ecosystems.
