Rear Sensor on Brake Fluid Reservoir Leaking
 

I was attempting to bleed my brakes (1984 300D) with a Motive Power Bleeder tank but could not get any pressure built up. I found that the rear sensor on the reservoir was bubbling out air and fluid. I pressed it down and released it a few times to see if it might seal but it did not. Do I need to replace the whole reservoir or might I try taking the reservoir off, cleaning it and getting the small testing pin to seal. I am thinking that maybe there is a bit of debris in there.

After a break I reinspected the source of the problem and I think that all I need to do is replace the rubber cap which is badly cracked. I believe that is where it seals, not at the pin underneath.

Replacement caps are available. Pretty expensive piece of rubber, but way cheaper than a new reservoir.

Any opinion about Meyle vs Genuine Mercedes? Meyle is about half the cost. Does not seem like much could to wrong with a rubber cap unless Meyle is using a material that will dry up and crack prematurely.

The same caps were used from about 70 through 2001 so almost any mercedes at the wreckers you should find a good cap.

Buy a new one. The last thing you want is brake fluid spraying all over the place when you are pressure bleeding.

You can avoid a lot of problems by avoiding pressure bleeding.

The problem is that my wife is not always here when I am ready to bleed the brakes so using the pressure bleeder will be handy, I think (and hope) doing it alone. I need to replace that rubber cap either way.

I used a vinyl cap which fit, used to protect threads on stainless-steel tube fittings. Free for me. But, unless you work in high-tech aerospace and such like me you won't run across them lying around. Be careful if you wash the engine w/ water since it can get in the brake reservoir thru cracks in those caps. Water rusts the innards of brakes, which is why I use silicone fluid.

Use the M-B cap, it'll outlast you .

Don't go crazy with pressure when bleeding ! 3 ~ 5 # usually works just fine .