Just wanted to post that I had a good experience with these guys:
http://www.thrashdriveshaft.com/import2.htm#MERCEDES
The u-joint on my C43 driveshaft was sticky and causing a vibration at highway speeds. These u-joints are neither serviceable nor easily replaced as they are staked in place.
These guys take the old driveshaft, replace the u-joint, carrier bearing, carrier, end bushings and balance and repaint the driveshaft as part of the rebuild. Cost was $367 including shipping both ways by UPS ground (they didn't stock my model so I had to send one in for rebuild). They turned it around within 24 hours after they received it and I intalled it Friday and can confirm success!
The alternative was to replace the entire driveshaft for $900+ so the rebuild was a good way for me to go. Anyway, I would not hesitate to recommend them to anyone facing the same problem - their service was great.