in my experience fuel leaks usually wont stop the car from running. if it starts that means you're getting some kind of fuel delivery and then it stops when the car dies.

i can give you plenty of rx7 related examples, but i dont know enough about the mercedes to condemn any 1 part.

you're looking for something that would prime the fuel system, and then shut off when the cars running. ie it could be the fuel pump primes when you turn the key on, and then never runs again, or the injectors stop working (check with a light?)

mike