I agree with the readers here. I had a k&n filter and it does flow better.
However I noticed a light film of oily dust collecting inside the air filter housing and inside the screen of the MAF sensor.......
It seems like a future problem......
Maybe a slight modification to the air filter housing to allow more air in using to stock filter would help.???

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2003 SLK 230 (85000)
1999 E300 Turbo Diesel (388,000)
1991 350SD Turbo Diesel (185,000)