1987 Mercedes Benz 300e bleeding brakes

The brake fluid reservoir has to be topped up with fluid. In the back of the reservoir there is a section for the rear break lines, if the reservoir is not completely full that section is empty and thus you won't be able to bleed the rear break. It's easily done by removing the little net cap on top of the reservoir (after you take off the reservoir cover), you will be able to see a little hole on the side of the reservoir from inside, you have to fill the reservoir with fluid a little higher than that hole (it will overflow into the hole and to the back section of the reservoir -- the rear brake section). Fill the reservoir up completely with fluid and then shake it gently, hopefully you'll be able to see the fluid is getting into the rear brake section of the reservoir. Repeat topping up the reservoir with fluid until the rear brake section is full. Now, make sure you bleed the brakes in the right order: RR, RL, FR, FL, i.E, you first bleed the brakes that are furthest from the master cylinder then the one after and so on. After every time you bleed one wheel, look at the fluid level of the reservoir and always make sure that it's full and hence the back section. Hope this will help.