Johnny Fixit

Hi all and thank you for letting me join. Many years ago we were about to board a ferry with our 2012 diesel when the brake servo packed up. In a panic i had a quick squint and found there was a hose or valve that was leaking which I deleted (OK, yanked off and stuffed back on the next nearest fitting..) in order not to miss our boat. It's worked fine ever since other than the pedal being very sensitive /fierce. No issue at mots etc. I figure it's high time I fixed it but can't remember for the life of me what I ditched.. Any clues what might give those symptoms? I looked for diagrams on line but there seems to be any number of (mostly very expensive..) different possibilities. The picture is of the only remaining valve I can see which is between the vacuum pump and the pipe running across the bulkhead to the servo.. Thanks in advance, Jon