It's my belief that there is usually very little to see and running it unloaded won't help much. With the drive axles hanging you are likely to cause vibrations.

The best view is experience. Experience gained through lots of wasted time doing a bunch of wrong things and from feeling a lot of u-joints (driveshaft out) that were then replaced with proper results. An experienced MB tech should be able to decide whether the problem is driveshaft or drive axle related. The only thing to do at that point is to pull it and feel the joint out of the car. If one gets to the point of knowing it is a driveshaft problem I would get an exchange unit from Beyer Motor Works in Mesa AZ (800-824-0809). We have gotten hundreds of them from them (mostly for BMWs). Some of the real hot rod BMW shops have been known to send factory new units to Beyer to have them gone through before installation. They remachine the center yoke to accept a replacable u-joint and do straightening and balancing par excelance.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician