It is and it's cheap ($30). In Germany though. I tried to use the later style door brakes on my 530 and you can't because of the front window guide. Also, the brackets on the car won't accept it.
Ditto on Kohler's post. I bought both in the last couple years. I learned the hard way that the 528i front door brake won't work and ended up buying the 530i door brakes too.
