So I think what I am looking for is #7 on this diagram:

http://www.realoem.com/bmw/showparts...90&hg=11&fg=18


I used to use a T50 to loosen and take the belt off but today when I was going to change the pulley my T50 didn't fit right. I believe the mechanical tensioner is a T50 and the hydraulic tensioner is an 8mm hex. Here is my hydraulic tensioner picture I took with my phone:



Here is the bolt taken out with an 8mm hammered into it to take it out safely:


Here is the bolt with the 8mm hex out of it:


Do I have to get it at the dealership or do you think I can bring it to any place for a replacement?