Yeah, I put lots of silicone underneath the track / frame too.
The slab was meant to slope away but that got lost in translation with the concreter and as a result has been poured dead flat / level, which doesn’t help of course…
I was thinking I could cut a grout like drain channel 2-3cm away from the door to lead some of that water away from the door.
Thank you for all your very useful suggestions!
Do you think cutting a draining channel into the slab just outside the door (instead of sloping the entire slab) could also work?