I know this is an old post but you can fix the e-brake easily by making sure it is released (not set), then adjust the cable at the lower end to allow the max slack, then you have to re-clock the arm but removing the nut and make a witness mark with a Sharpie pen on both the shaft and the arm to use as a starting point.  Then remove the arm and rotate it away from the cable only a couple of splines.  It doesn't take much.  Slip the arm onto the splined shaft and adjust the cable to take up any slack.  Try applying the e-brake and try to push the car to see if it is holding.  My 2008 650 was the same way until I did this adjustment.  Now it works fine.  It seems that a lot of them came from the factory with maladjusted e-brakes.  Just make sure you leave enough slack at the cable adjustment so the brake does not drag.  If it drags, it will get very hot and cause the rear diff lube to exit from the breather tibe and bellows under the rear bed.  I added a lenght of tubing to my breather and mounted the bellows up high behind my right seat along the cross bar.  This has stopped the diff lube dripping I was getting when the bellows was mounted in the factory location.

Hope this helps.