There is no spacer there. The nuts that hold the master cylinder onto the booster are missing. If the brakes work at all, I would be surprised. Don't drive it like that.
If you look at pic 1 below, I circled the nut that I'm referring to. I also placed an arrow in the pic that is pointing in the direction of the second one that needs to be installed and how tight they should be.
Here is a link that explains how to replace a master cylinder. I'm not saying yours is bad, but the link explains how to install/tighten one.
https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder
Again, if this is how the vehicle is being driven, I am surprised it stops at all.
Let me know what I can do to help.
Joe
See pic below.
Image (Click to make bigger)
Saturday, January 1st, 2022 AT 9:08 PM