At my workshop all dust filters/combination filters are changed regularly, sometimes will will see mould, usually on ML's.

Active charcol filters on the otherhand, I've changed 2 in the last 12 months. Advisors don't want to call customers at tell them they need a $200-300 filter ontop of a few thousand dollars worth of service, brakes and service items. The owners rarely want to spend that money when they don't get a benifit they can feel or see.

Charcol filters aren't worth it, combination filters are the way to go in terms of cost Vs benifit, charcol are way too expensive.

__________________
Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32