I just over hauled two of mine and they are not that difficult.

Clamp the pump in a large vice with the shaft pointing down. Put a large C clamp from the end of the drive shaft to the back cover. Be sure to leave the pully nut in place and just even with the end of the shaft to prevent thread damage.

Screw it in until the back moves in enough to get a screw driver behind the spring clip that holds the back in place. Pop out the spring clip. Remove the clamp. Make sure that the back come up evenly. Check the distance between the back of the pump and the top edge of the back to make sure it is even all the way around. Turn the pump over and rap it hard on the work bench. The back should fall out. There is only a single thin O-ring holding the back in place. Once the back is off the pump rotor should just fall out. Be careful. There are about 6 or 7 blades in the rotor that will also fall out. Try to keep them in the same slots.

As I remember you can drive the shaft and bearings out the back by hitting on the pully end of the shaft. The seal can then be removed out the front. Mercedes offers a seal and O-ring kit for these pumps but be sure to get the pump model no. before you go to the MB shop. The bearings are available at any big bearing supply company.

When going back together be careful with the back cover and the O-ring. Use some lubrication and be careful not to cut the O-ring. I tested mine by getting an old power steering hose from a junker and connecting it to the out put side of the pump and hanging the other end back in to the reservoir. Install the pulley and spin the pump using an impact wrench on the pulley retaining nut. I also connected a guage to the out put hose and checked the pressure. Mine ran about 1,000 psi at the speed of the impact.

These pumps dont really wear out but the seals do leak. There is a relief valve internally on the side of the pump. No need to mess with it since there is really no way to adjust it, and no need to try.

Off the car, repaired and back on should take 4 hrs. if you have all the parts ready. It is not a very complicated job.