This is one of the most awesome tanks I have ever seen. I hated to read that it started leaking. If you are using a silicone for glass it may not adhere to the acrylic due to the different properties of the materials. I was doing some research into the issue and found a little info that might be helpful on eHow.com.
"There are two different kinds of acrylic glue, one being a thin liquid glue and the other a thick glue. A popular brand for acrylic tank repair is WeldOn. You should be able to find this at a pet store and at some hardware stores.
Empty your tank of all fish, water and gravel so that is is completely empty. Move the tank outside so you can use a water hose to remove any sand, gravel or buildup that remains in your tank so it can be as clean as possible.
Use a towel to dry your tank thoroughly and allow it to air dry so all seams and areas can dry completely. Bring the tank back inside and prepare an area to work in.
Prepare the area you will be repairing. Use isopropyl alcohol to remove any oils from the hands. For acrylic that has a small crack, but is still tightly joined, use a liquid glue such as WeldOn 3. For larger cracks that exhibit
more separation, use a thicker glue like WeldOn 16."
It seems that whichever you choose is dependent on how large a gap you have to fill between the acrylic and the plumbing.
Read more:
How to Repair an Acrylic Aquarium Leak | eHow.com How to Repair an Acrylic Aquarium Leak | eHow.com
Hope this helps. Good luck!