Should be pretty easy, especially if you see the hex lug. If you have the hydraulic set up then a replacement pulley is available. If you have the mechanical then you need to replace the assembly. Both systems are interchangeable though. The hydraulic is supposed to be the updated system but I have an improved mechanical one (Delco pro) ready to replace my hydraulic one when it fails. I have a theory that the hydraulic one is transmitting more vibration at times.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)