Every Sprinter driveshaft (removed from the van) I've ever inspected has notchy u-joints. Every u-joint, every driveshaft, including my own 208K mile daily driver. No noise, no vibration. When it fails it will be replaced with a Dorman or some such.Everything seemed fine, but as soon as we separated the driveshaft from the rear diff we felt the bad notchiness/locking in the rear-most U joint.
I had also found 2 used complete driveshafts for a reasonable price semi-locally, both were obviously bad but not quite as bad as mine when I showed up to look at them. Unfortunate, but keep an eye out if you are buying used... I suspect most MB driveshafts will have this problem at this point.