I actually use engine degreaser, spary it on, let it sit, spary it off with water, rinse in soapy water then clean water, squeeze, softly, not like you're making diamonds. :yikes: Let dry, then I use the PJ1 foam filter spray oil. Light coat on the inside, heavier on the outside. Squeeze again to move the oil around, replace and ride. If you put too much oil on it, it'll start leaking down on to the swingarm and such, then you'll know.
Oh, and maybe a lite coat of grease on the seal that goes against the airbox, keeps the dirty dirt out. :cool: