I think i cleaned mine at like 30k and i couldnt believe how much dirt came out of that thing. I banged it on a table and i seriously had a small handful of dirt that dropped out. I finally decided to check b/c i had been doing alot of wheelin in the desert and knew i was injesting alot of dirt and dust, and i could feel the lack of performance from what i once had. I wont let it go that long ever again.
Cleaned mine today and it was filthy, it probably had 10-15k on it. My airbox was full of dirt and crap from the past few months But the back of the filter, mass airflow, and tube looked all good and clean. K&N FTW!!