Wanted to share this here, since there was no REP in ISTA and I did not enjoy the job; hopefully save someone else some headache.
When removing the master cylinder from the pedal on these cars(G12, G15, etc), it can snap the plastic retaining fingers that hold it in the brake pedal clip(BMW part # 35 00 6 891 934 ; BMW calls it a Ball Head Mount ) and you then have to replace the clip in the brake pedal. Getting it out wasn't terrible, just use a thin pry tool and you can separate the white plastic from the black painted steel of the pedal to release the 4 tangs holding it in place. If it breaks apart, no big deal; you are replacing it anyway.
Once you have the old piece out, the fun begins. These buggers don't want to go in! I was able to get it partially engaged by hand, but no matter how I pushed or pulled from inside the car, I could not get any of the 4 side tangs to snap in place. Finally had to stop and figure out another approach before I slit my hand on the sharp edges trying to force it in place. Plus I knew the fingers were fragile, so I had to be careful I didn't let anything slip inside the retainer during the install that would snap them off. Ended up using a pedal depressor to fully apply the brake pedal, moving the clip near to the master cylinder outlet. Then I could use a large blunt instrument to apply the force in the direction needed to get those 4 gnarly clips to snap in place. In the pic below, you can see what I am talking about because I still only had 3 of the 4 snapped in place when I took the pic. You can also see how close it it to going into place; they were all 4 that way, but required way more than expected to get them to drop in.
Just a tip. Happy DIYing!