My daughter's CLK320 (2001) had a similar problem at 103,000 miles. Occasionally it would stall while idling at traffic lights, but would restart OK. Finally it died in front of the house, and was difficult to start, and threw error code P0335. I replaced the crankshaft position sensor. The problem never occurred again. Now it has 146,000 miles.

I think I could have got away with just cleaning the sensor, because when I took it out the magnetic end had a few metal particles stuck to it.