My R53 recently started resisting going into gear -- still drove fine, it just was getting progressively more difficult to get it in gear. I changed the clutch/pressure plate/TO bearing in June 2024 and it's run fine until now. My first thought was that the slave cylinder needed bleeding which I attempted by pressurizing the brake reservoir with a Motive bleeder but I had difficulty getting the system to stay pressurized. Fast forward ... I noticed a fluid leak under the car and traced it to where the brake cylinder/reservoir meets the booster. Note #4 in the image below that is an o-ring that provides a seal between the cylinder and the booster. This is where the leak has occurred. Has anyone experienced this? On first glance it appear to be a PITA to remove and replace. Any recommendations? Thanks.

 

In my experience with other cars, if you have fluid leaking there it means the master needs to be replaced. There should be internal seals that prevent fluid from leaking past the master cylinder piston. If those seals start going out, you'll get fluid leaking down the shaft and out the booster connection. I am under the belief that o-ring only provides a seal for the vacuum in the booster, not against fluid leakage.

 

Makes perfect sense. Thanks for the reply.