I would suggest that you start discussing with them the fact that this car has a reaccuring problem that has been there from the start. Basically its not fit for purpose.
I would suggest that you ask them when they repair it next that you want a written guarantee from BMW/Dealer that the problem will not happen again. Suggest that due to the hassle you have had this is only fair!
At this point BMW needs to decide if they can fix the issue or replace the vehicle?
If my vehicle fails again, my leasing company are basically prepared to reject the vehicle based around a product guarantee. The manufacturer has had a fair chance to make the goods correct for use, and has failed to do so. Its within your statutory rights as a purchaser.
BMW E93 320i M Sport - Black Sapphire / Coral Red