I'm doing some maintenence this week and am going to the parts dept. to pick up some stuff. Just looking at the various things I need to do and am wondering what the maintenence schedule should be as far as changing (or cleaning) the filter element in the air filter? I have no reason to suspect a problem, but was wondering if that's something that should be done as a preventative maint. item? None of the books I have list a specific mileage at which it should be done.

This is a 603, 300D.

__________________
1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)