the drive shaft will have some longitudnal motion - enough to get the flex discs out, if it were solid I dont think the shaft will be able to absorb the slight movements of the transmission or diff. The U joint stickiness is bad news, you need a D shaft shop to stake a new U joint in place and balance the shaft again.

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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)