just spray it in a bag then put ya filter in and work the oil in with ya fingers onthe outside of the bag make sure ya cover it all but dont use tooo much oil cos it wont breath right and take ages to dry
and i find just washing powder and some dishwash liquid cleans filters good and thats what is reccomended been doing it for years just wash all the soap out after washing let it dry fully,oil it up in a bag the let dry again and definetly a little but enough grease just on the rim of where the filter sits against the airbox to get a nice seal to easy..