Heres a thought..sell it as is to someone with reptiles or something, and keep shopping for another tank. If you patch it, its probably gonna break..if you replace the panel, its going to cost ALOT, then you have to change it, re silicone the tank, and hope it doesnt leak, or break in the process of replacement.
Oh, and DONT try to use plexi-glass and silicone, it wont hold.