Hi Greno, I have a very similar problem. I wonder if you would mind clarifying something for me. My Kudos cubicle is leaking at the fixing post, I believe because the shower tray has dropped a millimeter or so, and pulled itself off the sealant to the tiles on the inside.
But even before that happened the sealant on the outside edge around the tray had gone horribly mouldy. The inside has not been sealed (correctly, I believe), apart from the width of the fixing post itself. As far as I understand the fitting instructions that should not be sealed either. Just the inside upright edges, and round the tiles.
But that means water is constantly trapped under the bottom edge of the frame. Surface tension stops it running back into the tray.
Did you get the same problem ? Even with my leak fixed at the corner, I don't see what will stop it. I have currently removed the outside sealant and water doesn't escape, but it doesn't dry up in the gap either ! I don't know what the outside sealant achieves ?
Also I don't know what you mean about the fitter not sealing the tray at the fixing post ? Do you mean outside ?
Sorry to be a pain, but it's just that having fixed yours, you might know what I am talking about !