I've noticed that (after days of continuous rain) the floor carpet of the back passengers is wet on both the left and the right side (L322 2010). It seems it starts at the sil trim.

The drain tubes for the sun roof seem to be working properly, I've checked then in the summer. Can't find any wet spots in the roof lining.

What else could I check to find the culprit? Door seals?

My 2012 WM stood for an afternoon in really heavy rain and I found water on the seat and perhaps on the floor too. The problem was with the positioning of the door seal, it was repositioned and thereafter no problem, done by dealer under warranty. Only Range Rovers since 1988

You could check to see if the drain holes in the bottom edges of the doors are clear.