The drive shaft felt OK when I bought the vehicle but with 170,000 miles on it, it would be better to take it apart and put some new U joints in it.
They actually still looked good, the grease was hard and black, there was some brinelling from the needles but it would have lasted a few more years. The rubber donut looked fine, so I just re-used it. You can still buy new ones, they are used by BMW on some of their older models.
I bought some new universal joints for it at Lordco, they are not listed under Vanagon Syncro but under PTO shafts, size is 27 mm x 70 mm. Before I paid for them, I checked with a small file if they were heat treated, a lot of u joints are soft and won't last at all. They came with a grease nipple and 2 circlip sizes so you can take the play out of them.
I had to machine the grease nipples so that they would screw in deeper, they won't fit as supplied.
An often overlooked problem with the later style Syncro drive shafts are the bronze bushings that are located under the rubber donut, they wear out and cause vibrations in the drive line.To remove them, I put a thread into them, 1'' just fits, then used a piece of ready rod with nut, washers and a piece of pipe to pull them out.
Mine had a lot of wear and corrosion and I had to machine 0.035" off the shaft to clean it up, I made two new bronze bushings and pressed them back in the drive shaft. Next I fitted it all back together, I had to use the thicker circlips in order to get all the play out of the cups.
On the Syncro, it is important that the drive shaft is well aligned, both the tranny and the front diff flanges have an angle of about 4 degrees. If you do an engine conversion, and the engine hangs too low, you could end up with some vibration. Another thing to watch out for when doing a conversion is that the original VW engine is slightly offset towards the driverside, about 17 mm, if the new engine is installed in the center of the engine compartment, it will put another angle on the drive shaft that is not compensated for by the front diff and it may cause a vibration also. It is too bad that VW didn't put a CV joint in, one would have been enough.
On a two wheel drive Vanagon it is not that critical if the engine is centered, the axle CV joints will compensate for that.
Total cost for the U joints was about $ 80.00 and it took me 5 hours to machine the parts and put it all back together.