Leaky window in toilet compartment

Hi, we have been finding increasing amounts of water in the shower tray of our 2004 Symbol. It appears to be coming in through the small oval side window as we have seen it dripping down the wall. Hubby has used loads of clear sealant outside to try to make it watertight but it’s still coming in. Question is, is this a known issue and if so is there a fix for it?

Hi Bun
Welcome to the forum from Bridington,should get some help when others are up.    
Boaby