ABS cars have to be pressure bled, a mityvac doesn't work on them.

The ABS pump is that thing on the drivers' side directly behind the windshield washer tank. It has all the hard brake lines running to it.

I never had any trouble bleeding 210 cars using the master cylinder method. Does this car have the divided reservoir where you have to fill it all the way full before the section for the rear brakes receives any fluid? That is a common problem on the older MB cars, but I am not sure when they changed to a single chamber reservoir.

How confident are you that the master cylinder is good?