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Anyone ever find oil in the brake booster chamber? I suctioned out about an ounce of what seemed like watery oil in the course of a brake overhaul project. Back of the master cylinder is bone dry. Does the check valve by the intake manifold fail and allow oil vapor through? Thanks.

^ yes, this has happened to me and I can confirm swapping the one way valve fixes the issue

Are you sure its not brake fluid?
My master cylinder was leaking fluid into the booster.

Back of the master cylinder is dry and it seemed like watery oil and smelled like oil. I suppose if the 1 way valve is bad, residual vacuum in the booster could pull vapor with oil residue back from the intake log which would accumulate over time. I'm replacing the master cylinder as a precaution and the 1 way valve as well.

I just had that issue with Camry, check valve (as Bizz said) fixed that.. but if you want to eliminate oil in the intake all together a catch can is always great to remove most blow-by .. I have them on all cars and intake manifold is never oily anymore..

Thanks HiLux30. Removed the injectors for cleaning and wow is there lots of oil residue in the intake manifold and runners. Valves are spotless but I have to believe the accumulated gunk reduces air flow efficiency a bit.

What brand/ type of catch can are you using on the BMW? And where did you mount it?