On the 4 door, open the back door and pull down the door seal from the back top corner which will reveal the edge of the headliner. Pull the headliner back -will be glued down but if old it will come away easy. Also might find you have to remove the handle grab.
I did this and to my horor:
Going to have to cut the rust out no matter what. Just hoping i can find someone that can repair this and not cut a whole leg off to pay for it.
Its almost as bad on the left side. With this it meant that the water ran down the liner of the pillar (had to remove the insulation which was toast) and down the side of the seat to pool on the rear foot well.