*** Update ***
So its clear that the stupid 'mastic strips' the "professional" used are useless, after I peeled away could see the grout behind it (although neatly done) showed signs that water had been absorbed.
Got everything I need to properly seal, just a final few questions.....
1. told not to put sealant over the grout on the two vertical joins where the 2 tiled walls meet the mosaic wall - can I confirm this is correct? Seems odd as grout is not waterproof- or should I try and remove the grout and replace with sealant? (rather not unless its a must)
2. My shower door is Aqualux - I'm also told the inside horizontal (where the bottom of the frame meets the shower tray) should not be siliconed - but the person I hired has used something (again looks to be some sort of cheap clear plastic tape) - should I remove this?
3. Was told to silicon the verticals (where the shower door frame meets the tiled walls INSIDE and OUT, and the horizontal (where the bottom of the shower frame sits on the tray OUTSIDE only) - sound right?
Thanks ! Feeling more optimistic this will fix, as saw another helpful post on here which looks suspiciously like it might be present in my shower...
"lack of sealant under the shower enclosure...where the enclosure bottom corner meets the tile and the tray. if there was no sealant there when u installed it then what happens water runs down the enclosure/tile joint ...gets behind the enclosure ..runs to the tray and out the back