I am finally back to where I left off. The upper left corner facing me where the brake booster nut is located behind the brake pedal is stripped (using 13mm socket six point, and tried to use 12 point 13mm). The other nut located below on the right side brake booster was removed.

I was researching for brake pedal assembly removal instructions so I can gain more access/room to get to that brake booster stripped nut. I do not find any information on the removal of the brake pedal.

It seems to me, at this point, is to leave the brake booster alone and reinstall all other parts back to its original place. Using the newer brake master cyclinder and put in the push rod inside the brake master cylinder. Screw with the nut on the brake booster with the push rod inside the brake master cyclinder and hopefully it would work. According to the technical article on the brake booster in the comments section falling gator (username), push rod inside the master cyclinder and connected to the brake booster. https://www.pelicanparts.com/techarticles/Mercedes-W124/83-BRAKE-Brake_Booster_Replacement/83-BRAKE-Brake_Booster_Replacement.htm.

I think this is the option I should take, unless someone has better ideas in resolving this issue. Any comments, feedback, advice is greatly appreciated. I will follow up on my progress.