Mine is over two years. AFE Pro Guard 7 gold. Clean in a bucket hot Simple Green, rinse, air dry, reapply oil. I have two of them so I can simply put on a clean one and not wait.
One other thing, I'm not using the stock air box, mine is the AFE aftermarket w/torque tube. I started out with the stock replacement AFE type. You can also contact AFE support directly, good people.