A little maintenance goes a long way.

[209]

K & Ns can hold a ton of dust but don't let dry spots appear. Rinse from the inside out and reoil evenly. Been using them for 40 years.

[patrickt]

Any chance the brown stuff that comes off the filter is just the oil that's on there and it's not really a ton o' dirt? Why wouldn't K&N want you to clean it more often than 50k miles if they're selling the cleaner and oil to do it?