Open the door and see where the lock catches on "the car bit" rather than looking at the door, they can be moved if loosened first.
They are called the door striker.


This bit mate

Striker%20Stock1.jpg
 
Funny I just noticed this on mine too on the rear passenger side, certainly wasn't like that before :blink:.

What kind of tool slackens those Striker bolts then, looks a bit like torx?
 
Before getting into a conclusion please check wheather it is the problem of the door lock or the seal.

I think adjusting the door lock will solve the problem