I have a similar problem, no reverse at all.
For a while the reverse would not engage or was slow to engage till I blipped the throttle then it would catch. So it seemed to be a pressure issue. Now it is not engaging at all no matter how long I raise the idle. I get a little reverse motion but not enough to move the car on level ground.
The fluid is up to level, clean and all foward gears engage fine.
My friend is a Benz mechanic for a dealer and he says it might, I repeat might be an adjustment on the pressure regulator, but more than likely it is a bad reverse clutch.
He is pulling the pressure regulator adjustment procedure for me. Any merit to that?
Also, if the adjustments don't work can I throw some "Mechanic in a bottle" into it so it will engage a few more times so I can dump the car at a used car lot? Sawdust even?
I do not want to replace the tranny, I would rather sell the car. I think I have have had enough of "Riding behind the Star"
I will go back to BMW after this....at least I know those.