Why is the little filter inside the air filter housing that goes to the air pump? not replaceable? it seems it is paper and mine is rotting away. when I go to the parts dealer, not the dealership, the computer says it is not replaceable? Did the engineers think this paper would last forever?

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual