The problem with your repair is as follows.
The round surface that the allen screws into has a relief cut into it so the fluid CAN escape when the orings leak. IT is SUPPOSED to leak when the seals fail.
If you stop up the leak as you did, you are putting hydraulic pressure on the housing which may cause failure, no know, liquids are not compressable.
The B-1 reaction valve is the barrel behind the bolt that is leaking. I have replaced about 1,000 of them. They can be purchased for about $100. or so and install in about 15 minutes. Problem solved. Your dealer is full of crap.
I have only seen one done wrong by another tech and I corrected it. If you buy the NEW valve and o-rings, it will go in smoothly.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS