Hey guys, ive had my K&N in my car for about 8k miles or alittle more and have my air silencer removed. How often should the filter be cleaned? I can't really tell if its dirty or not. Also, do places like, Pep Boys, Autozone, and O'Reilly sell the cleaning kits? I know it has to be cleaned and re-oiled and lef tto dry for a day.