power brake unit - Question

[FLYINGRX7]

Hello,
I have removed my brake master cylinder and have checked the parts, the washers etc. are worn down - so need replacing- not a problem.
However, after looking at the power brake unit I have discovered that a nut was loose on the unit ( the one on the rod that inserts into the master cylinder).
Could this be the reason for brake fluid seeping between the master brake cylinder and the power brake unit ?
If I\'m correct there is no fluid in the power brake unit, but would a loose rod have any effect on fluid retention? ( cracking sentence;) ).
Any help or advice would be gratefully recieved.
Happy Easter