excellent writeup from DBU @ Bimmerfest on tensioner replacement:
https://www.bimmerfest.com/forums/at...6&d=1532363351
Short story is that there was one tensioner design thru 2007 that had a thicker head and less travel. Then from 2007 to 8/2016 a newer design with thinner head and more travel. Then from 8/2016 on, a newer design that look the same on the outside but with a stronger spring (not sure if it is stiffer in lbs/inch, or more preload, or both, but whatever - it was modified to be stronger for a reason).