Wow, what a pain in the butt.
You can no longer obtain the original tensioner pulley or the assembly from normal parts houses. BMW will only sell you the new hydraulic replacement assembly for about $250.
AZ, o'rielly, Advance only have a replacement pulley for the hydraulic assembly, they don't know that, but that's what they have. (It won't fit the orig mechanical assembly)
The BMW dealer hooked me up with a source from BAP-GEON in Houston for a new in box original mechanical style. $70
I'm back in business.
Think I'm going to move forums. Good Luck.