the raised boss should go into the driveshaft or gearbox flange depending on which side of the disc we are talking about, the driveshaft is slightly bent at the sloping angle and it can become a wrestling match to seat it but it should just self align and be pulled into the hole once you start tightening the bolts.

What brand flex disc are you using? and be sure to face the disc correctly, the side that says diese seite zur gelenkwe means this side towards driveshaft. Or the transmission shifts become a little yanky

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)