I came across a test done scietifically using a filter in a stock air filter cannister housing for the 1982-1995 non-turbo 6.2-6.5 liter diesel engine: one filter was the AC A644C with an oiled foam wrap, one was the K&N 1690, the other was the Amsoil Type 52 an oiled foam with a deflector plate. Using a blower to get a consistent draw of 540 cfm through the filter cannister, the tester used a consistent grade of dust size-wise and weight (4 oz. flour-like with size less than .0049", 1 oz. .0049"-.0082", 3/4 oz. .0082"-.0098") fed into the intake of the cannister - similar procedure used by testing facilities. The amount of air flow restriction was similar for all three filters. Results, the Amsoil caught by far the largest amount of dust and far less would reach the engine, next was the AC with the oiled foam wrap, and last was the K&N with the AC just slightly better than the K&N.
The tester commented that the Amsoil filter had a plate on it that is suppossed to be located at the point where the air from the intake strikes the filter - he theorized that this plate deflected high-speed particles and allowed the filter to trap them. The tester was not associated with Amsoil (I've looked a lot at Amsoil products and it is hard to find info from sources that are not associated with Amsoil - independence and objectivity of opinion/testing is what I'm looking for). Read the article at
www.lubespecialist.com/airfilt.htm
One downside about Amsoil air filter and other filters - none are made for the older M-B's (I did not check availabilty for later model M-B's). That said, I have some inqueries out to see if one of the Amsoil filters for another application can be adapted to my '77 300D (which would also fit several other M-B's up to 1985). Dirt through the intake track will cause excessive wear on the cylinder wall to piston contact area leading to excess oil consumption and excessive clearances leading to the need for an engine overhaul before needed.
Alternatively, replace the paper element filter (OEM type made by Bosch, Mahle, Mann, or Knecht bought from FastLane) a bit more frequently than required and if in dusty conditions much more often. Importantly, thoroughly clean the air filter cannister before opening it to reduce the amount of contamination and filth on the cannister entering the interior of the cannister. Also, make sure the seal between the air cleaner cover and the cannister is good.
Good Luck!
Tom