Stillen uses K&N Filters on their intakes. You should to purchase a
K&N Filter Recharger kit to have everything you need to service the filters. Any local auto parts store (~ $20) or vendor should have it.
Follow the directions in the box. You do not want to over oil the filters as it will impede the flow thru the filter....and make a mess behind your fascia.
Its a very easy process and takes about 15 ~ 20 minutes to do. You need to lightly coat the filters and let it soak in the filter media.
I generally clean my K&N Filters once every 3rd or 4th oil change (but it can really vary on where you live, the time of year, etc). For example, if you lived in a very dusty area or on a dirt road, I would clean it regularly. If you have an oil cooler installed, I would service the filters at the same time that you service the oil cooler (I also remove and drain my oil cooler core every 3rd or 4th oil change).
Just my thoughts...