2001 CLK320 103000 miles

The car occasionally stalls when idling, or doesn't start at all. When it starts, the check engine light stays on for a while and then it goes out. The last time it stayed on I connected a code reader and got P0335 - Crankshaft Position Sensor.

1. Does this mean the CPS is defective, or could something else related to the sensor throw this code?
Looking at it it looks like it has never been touched in its life.

2. Could metal particles and debris collect on the sensor and cause this error code? Is it worth cleaning and reinstalling it, or should I just replace it?

Thanks