Many of these don’t need it for a long time. At least on these MB cars, the driveshaft is essentially straight so there is no flex or movement unless some mount (engine, trans, diff) is collapsed. I had the driveshaft out of my 93 300SD which had about 291K miles at the time, and it moved smooth and perfect. I think for at least some of these cars, if they have t seen too much moisture or salt, the u-joints just don’t flex enough for it to matter, assuming the rest of the driveline is actually aligned.