Thank you all for your comments. If when I suctioned fluid out of the reservoir, new fluid failed to go into the rear chamber, that would easily explain why no fluid is reaching the rear calipers. Dumb question...on some cars the rear chamber goes to the front calipers. Does the rear chamber of the reservoir go to the rear calipers on the 300e?

But the configuration of the reservoir has the fill port toward the front. When I pull out the screen, I can see that the reservoir is separated somehow into front and rear chambers. But if you pour the fluid into the front chamber, it must fill the rear chamber too.

I just went out to my shop and looked at the reservoir with a flash light. The reservoir looks full from front to rear. I'm not losing any fluid. And when my wife pushes the brake peddle, the master cylinder is pushing air out (somehow). The bleeder tube on the caliper bleeder blows bubbles into the fluid in the cup that accepts the old fluid. I'm perplexed that the pump can blow air instead of fluid, if fluid is in the reservoir.

This car had brakes until I bled the system. I've bled the brake systems on many cars. I've done it 100 times. I think that I'm doing something wrong. I doubt that the master cylinder simply failed while being bled. This is most likely to happen the first time you work on a new car.

It's very possible when I siphoned out the old brown fluid, that I might have somehow allowed the rear chamber to go dry. I was watching the level in the front of the reservoir. But even so, once the reservoir was full, the pump in the master cylinder should take up the new fluid.

I think that I have fluid in the rear chamber. How could you fill this reservoir and not have fluid enter both chambers?