You have two problems.
1. The cracked frame.
2. The leak.
The cracked frame is only cosmetic. The plastic does not have enough strength to be considered in the integrity of the tank.
The leak is caused by a problem in the silicone seal. You will need to locate the leak and inspect the seal in that location to determine a course of action. Either the fix is to dry it and add a blob of silicone or you should strip out that location for a reseal job. If other areas of the silicone are showing signs of lifting then you should reseal the whole tank.