You might consider something like a "Speedi Bleed"...a $100.00 pressure bleeder. I've used it on my '91 300-SEL with great success.
Also try bleeding the right rear, then left rear, followed by right front; then left front. I've had no success bleeding modern vehicles using the old "2 man" method. The parts connection on this site may sell them.

Regards....Mike Murrell