Under normal use, K&N recommends that you clean and oil the filters every 50K miles.
I prefer dry filters. No oiling kit to buy and no risk of over-oiling them; doing it once a year is just begging for over oiling if you ask me. Just blow out the filter from the inside with an air compressor every so often. Some people do this every oil change. Others will do it every 10-20K miles since you have to take off the bumper for these intakes. For a deep clean you just have to soak the filter in some water with a little bit of Simple Green and let it dry completely
