I am putting back together a 1977 CJ360 (similar to a CB360). The air filters are hard to find new so I was thinking of cleaning them. They are mainly just dirty but do have areas where, what I assume is petrol, has dribbled into the air box and been absorbed by the filter. They seem to be made of cotton. I was thinking of washing them in petrol to remove the grease build up and then washing in warm soapy water. I was wondering if this is the right process or if there is a better way to clean them, any advice would be great.