You would get bigger quad trims if you try a local glazing/plastics company
I removed the panel on the bath and the bath isn't attatched to anything... its legs are fixed the the floor and there is a timber frame on one side of the bath... I was going to try and move the bath over but didn't want to make more problems than im solving lol but there is a lot of movement.It's not always the tiling/tilers fault that these showers leak.
90% (a fact in my head), of problems are caused by movement of the bath or shower tray. Most plumbers do not support these properly, or becoming more common fix the bath/shower against a tiled wall, so it's only silicon holding them together.
Every bath or shower i do i always check for movement and they always move.
Easily fixed with battens wedged under bath!