"Window Doctor" for leaky double glazed doors? Recommendations needed

[LuLu Too]

I have uPVC double Glazed Juliet balcony doors that have been letting rain in throughout the winter.

I've had extra mastic sealant added and the roof checked, but driving, horizontal rain still gets in, somehow, underneath the door frame, causing damp patches on the ceiling in the room below.

So, can anyone recommend someone/ a company who can do remedial, repair work?

Worst case scenario, I guess, might be that the whole door/ frame needs re-fitting...

Thanks for any suggestions!