Do I spray the oil on the inside, as well as the out side or just the outside?
I have never cleaned a K&N air filter before because for some reason I waste my money and buy a new one almost every month. I got this thing, that I like to alter my CAI all the time (sometimes a certain setup may need a larger or smaller filter).
I maintain 2 microturbine power generators at my work that use large K&N air filters and I oil both sides of them. I let the filters sit overnight to let the oil soak completely into the cotton pleats. Make sure you don't use too much oil.