I bought a Speedi-Bleed for this purpose and have used it successfully for the past 5 yrs. Fluid gets flushed annually. The product seems to get all of the air out and I end up with a firm brake pedal each time.

There are all sorts of gadgets such as this one out there. Mine has a line that connects to the spare tire. The other end of the line connects to a special cap that screws on to the brake fluid reservoir. You pour a qt. of Dot-4 or whatever you like in a plastic container, then open a valve to create pressure that flows the brake fluid. The 4 bleeders screw must be opened of course.

Some members here have posted instructions for going the home-made route if you're so inclined.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"