Advice? Stay in their face until you get satisfaction. Don't give them the slightest hint that you will back down.
You paid lots of what I expect is hard earned money for this car, if they can't fix it, they owe you another car.
This is MB's problem, not yours, stick to your guns.
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in