Brake leak issue

Hey everyone,

I’m getting ready to work on a 2000 Pontiac Sunfire for a co-worker. They told me that brake fluid leaks out where the fluid reservoir attaches to the master cylinder. Could that be a bad master cylinder or something with the brake booster? It looks like there is alot of sludge in the reservoir.



I probably is where the reservoir meets the master cylinder. Those things have round seals in them to mate them together. Not sure how it is on a Pontiac but very often they just pull off after loosening one bolt so you may be able to see what’s going on in there.
Brake fluid is very corrosive to it sometimes does do damage to the booster.

Just a warning: you are takng responsibility for the most important safety item on a car. You asking this question makes me wonder: should you be doing this work? It’s great to try and help your co-workier, but if you do something wrong, do you want that responsibility? Do you want to be sued?

Gotta ask…

I don’t have an issue with being able to do the work correctly and safely. I’ve just never seen or heard of a brake system failing here. I’ve done many brake jobs for people over the years and have never had an issue. I always double check myself as a precaution.


I have seen it once on a Nissan. Maybe it was a factory defect that just took a couple of years to show up. The new seal has held a lot longer than the original did.

I have a new master cylinder with reservoir ready to go on tomorrow. I’ll pre-fill the master cylinder, swap them out, then completely bleed all the lines. New brakes will go on after that.


OK, just checking. Sounds like you have it figured out.

Bench bleed the master cylinder before you install it.

Stick your finger in the brake fluid of the leaky reservoir and see if it has any type of oily feel to it. if so, something other than brake fluid has been added and caused the seals to deteriorate and leak. If that’s the case, this leak is just the beginning of your problems.