crank position sensor replacement on 2001 Mercedes-Benz E320

where is the crank position sensor located, is it hard to change , are special tools needed

Asked by for the 2001 Mercedes-Benz E320
Driver's side rear of engine on the engine block behind the oil filter, it is secured by one allen key screw. Just under an hour to change about $100 to 120 for the part.
i have to go under the car? cause i dont see it? at the top