When I replaced the MC on my car my rod did not have one on it. I couldnt find one so I just stuck the rod back in.. I have not noticed any issues not having it and its been that way for 2 years.
the issue is the rubber retainer keeps the rod inside the MC.....there have been many case where the rod has fell out of the master cylinder...and look mom no brakes..
if it is not machine or you dont have the little rubber.....just fill the void with rtv
