Well my car was randomly stalling on the streets and was pulling code P0335 which means "Crankshaft Position Sensor Circuit Error". I had problems starting the car after it stalled and I could restart it after a few minutes of cooling down. Apparently the Crankshaft Position Sensor is affected by heat when it fails. I did a lot of research on MBWorld.org and found many threads on the subject:
http://forums.mbworld.org/forums/showthread.php?t=76431
I pulled it from the service manual already. It just says remove connector but it doesn't say how. There's actually a small clip that attaches to the part. You have to push the rear end down and pull it off. Don't pull on the wire. Then after you have to take a star socket and remove the retaining bolt.
The Mercedes Part # for the Crankshaft Position Sensor is 003 153 27 28. Unfortunately, no local autoparts store in Austin carried it. The average price for an aftermarket part is $80-90. I went to the Mercedes Dealership to get it and the part has been updated to part 003 153 28 28 and it cost $153.90 for the original Mercedes part.
I would say overall that it's easier than replacing a spark plug, but it's in a tight space and you can't really see or maneuver too much. If you're good with mechanics and you have the right tools it should take about 20 minutes to replace, not the 1.25 hours of labor quoted to me.
I've included a bunch of pictures so if you guys ever run into the problem.
Picture #1: Bolt, Star Socket, New part on the left, Old part on the right
Picture #2: Socket, Top of Screw, New on left, Old on right
Picture #3: Rear of engine where sensor is in the center of picture
Picture #4: Picture of where the sensor goes and the bolt hole
Picture #5: Picture of cable
Picture #6: Picture of sensor installed and cable attached
Picture #7: OBD II - no errors