I know no one (touching wood) that has got the mileage out of their Air Mass Meter that I have. I am (right or wrong) attributing it to my frequent air filter element changing, and VERY thorough cleaning of the airbox with every service.
Many folks that have installed K&N's have wrecked their AMM's so I would guess that (K&N's move more air and more "stuff" too) the AMM is damaged by particles flowing through the device.
When my Dad's 98 C230's AMM went, I found the airbox filthy. His car had codes P0170 and P0171.
1998 C230 "Black Betty"