Recondition brake booster leaking brake fluid

[twosixtyzed]

I had my brake booster professionally (i.e. not me) removed, reconditioned, reinstalled in February 2026.  The car's sat in my garage since driving it 5mins back from the shop.  I noticed it's leaked about 1/2 the fluid since then and taken the paint with it. The master cylinder rear seal seems to be leaking at the master cylinder-to-booster mounting flange?  The nuts are all tight. It's not leaking from anywhere other than where the blue arrow and red arrow are.  I can't get a better read on it than that, it's an awkward spot.

My skill level is basic but willing to give things a try.  I could drain the fluid, undo the two master cylinder nuts from the facing plate. Then the two nuts on the booster then....what? Is it a gasket that wasn't seated right?  

I am inclined to go back to the mechanic and politely ask if he can take a look, but at the same time, it's my car, I gotta take responsibility and put some effort in but I don't want to c0ck it up and make it worse.  You know, a novice coming in thinking he knows more than he does.  I don't want to be that guy.  

 

[RichyRich]

Given you paid to have it restored (which I assume was the bore only because the outside looks unrestored), I’d take it back, tell them what’s happened, and see what they say.

Worst case, they don’t accept any responsibility, and you either have to pay them again / more, take it somewhere else, or do it yourself. But, at least it gives a chance they might fix it under some sort of warranty, or provide some explanation that might help decide the way forward.

It would cost nothing to take back to see what they say…so nothing to loose, really.