Does your door rattle like something is loose when you shut it? Do your doors not stop when you open them? Chances are your door brakes are totally shot.
Fortunately, in 2005 BMW released a new and improved Door Brake to replace the original design which easily failed after a few years.
The new part number is 51 21 0 301 601
It replaces 51 21 6 450 014. These use a spring mechanism which was used in the later first generation 3 series E21 doors. They have two detent stops which keep the door held in place in a way the old ones never did.