1) I'm, not sure you have a problem. There are a number of systems on the car all which talk to each other on the "CANBUS" wiring harness. you many be trying to restart the car so quickly ofter turning it off that the systems are not having time enough to settle back to their starting position. THAT IS JUST A WILD *** GUESS, but if the car is allowed to shut down and then wait at least ten seconds before restarting do you still have this no start problem?
2) Stay with Bosch or OEM Mercedes electronic replacement parts. Other brands have been know to cause problems on our cars. Camshaft part numbers are:
MB A004 153 6928, Bosch 0 232 103 050.
3) A code reader is a necessity with these and newer cars; otherwise you are really just taking guesses, perhaps educated guesses, but guessing non the less.
4) Change/fix one problem, part replacement at a time. Doing several repairs simultaneous just complicates the procedure.