Can anyone share some info on the brake booster hose and where it connects to I will ofcourse purchase a new one . Trying to understand why after so much engine work done VSS etc spark plugs. I'm still getting 9.5 mpg on the computer idrive and cluster ... first I will start with this Mickey Mouse nipple they put on my brake booster

Where does the real hose go and where does it stop

2008 x5 4.8 103,xxx miles