The U joints can be changed. How involved depends on the type of drive shaft in the car. The later cars have a swaged in ujoint that is best handled by a shop that specializes in this kind of thing. It also presents a bit of a challenge on balancing the drive shaft.
It appears the changes occurred for the three different transmissions on the 250 SL:
For automatics at VIN ending 2468
For Five speed at VIN ending 2472
For Manual at VIN ending 2525
This is according to the list published by Mallory, in Mercedes Collector - Published in Pagoda Notes Volume 10 no 4
