I have never understood why the manual shut off did not have a cable to the inside of the car... who, in an emergency , is going to have time to pull the hood latch, then the front latch.. then push the off lever....
As the owner of an identical car all I can say is that you will have a new engine in about the most perfect automobile ever produced.... and I assume your son will learn a lot about Mercedes engines by the time this is over... check out the total cost of a new POS ... and figure in the finance charges... and you will still be $15,000 to $20,000 ahead of the game... and still have a car which CAN be fixed... as compared to so many of the new ones....