My 2000 Mercedez Benz E320 has a start issue:

does it crank but not start? fuel filter is the cheapest quick attempt to rectify the situation, best way to check, turn the key to acc/almost start but not crank, let it sit 4 or 5 seconds, turn the key off, do that again, and then off, and then try to start it, (this allows the fuel to build up the correct pressure prevented by a clogged filter or weak fuel pump), and let me know

I am almost certain that it is the Crank Position Sensor. I had the same issue before and had to change it. The part is about $50 - search on the web for it - and isn't that hard to change if you have some rachet skills. Or, you can pay a local mechanic 1 hour to do it.