R75 saloon - rear door sagging

[Spôôk]

Well sagging is perhaps too strong a word, but it is hanging about 3 mm. Which means that I have to close the door hard. It is actually the only door with the problem.
Has anybody got an idea of how to fix it?
Spôôk

[Pete]

Must admit I have never heard of the rear doors sagging before. I would check the hinge pins for one to be getting on with.