OldSD,

Did you solve your problem? I am re-doing the brakes on my 107 chassis, and I experienced the same issue when trying to pressure bleed the system- hook it up, and fluid flows pretty readily out of the master cylinder reservoir- took awhile for me to notice that the two plastic caps with low fluid level sensors (on either side of the reservoir fill cap) are split at the threads. Must be where the fluid is coming from when the reservoir is pressurized.

Again, were you able to solve your problem w/o replacing the entire reservoir? Different chassis cars, but the brake systems are pretty similar through the years-

Thanks! JAS

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94 E320
71 350SL