When I got my car 2 years ago, the parts place told me to replace the secondary filter maybe once every 30,000 miles. The other day, I was talking to the same place, he said "should be changed every 2-4 months"! Some of you fancy guys out there might have the Mercedes maintenence schedule, but I didn't get that with my car.

How often should that be changed? I change the primary filter when it gets dark.

Thanks,

Jeff 1991 300d, 118k