I am looking for advice from an Audi expert!

I have a 2008 A6 Quattro 3.2L with no modifications (regular service at dealership, excellent condition). It is currently at 72,000 miles. For the past 10-12,000 miles, I have had an intermittent problem with the check engine light. The light used to go off once every 60 days, now it occurs weekly. It is always the same error code (and only one code) -- P0390: Camshaft position sensor, Bank 2. In general after running the car through 6-10 cycles (turn on - drive a few miles - turn off) the light turns off ... only to return within 3-5 days.

The dealer said he replaced the sensor, but the fault keeps returning. The dealer said it is an "intermittent problem" and I don't need to worry about it. However, I am unable to qualify for my State inspection due to the check-engine light not clearing. In addition, it seems a bit strange to get this error constantly.

What are the diagnostic procedures to figure out what is going on? What does this sensor tell me? What are approaches to pinpoint the problem and then repair or replace the part causing the error code?

Thank you in advance Audi-ninjas!