Heheh, seems like every time I see a W-body in a garage it's for a rear brake job!
I'd suggest bleeding the whole system, being sure to pump the pedal at all 4 corners (gravity bleeding doesn't work well in my experience). Bleed the left front, right front, left rear, and then right rear (going cloest->furthest from the master cyl). Pump the pedal about 10 times after you quit seeing bubbles just to be sure. I would be extremely surprised if that doesn't solve your problem!
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