2000 Mercedes Benz C280 How to replace crank position senso

As i've noted from my previous question, Engine hard to start at times, would crank but not start, No code was pulled, sparks ok, fuel ok, battery ok, And from reading other questions and answers, One said that crank position could be the problem. But when I looked for the sensor online it came with two engine number series, How or where do I find the engine serial number for my car? And do you have the diagram for it? (I meant the diagram for the location of the sensor)