All those years ago on my bikes i used to use petrol as it disolves and or thins down the oil. Let it dry then spray with the recommended oil.
Oil repells water and dont mix, it may push the debris further into the foam. Some form of cleaning solution that dries out, meths, petrol, trichlorethane doh..
Some oils were like grease BelRay. The only purpose of the oil is to attract debris/dust, which of course it clings to.
Its a fine art, too much oil and it restricts the airflow, too little and you are relying on the foam to catch any debri/dust.
Lets face it, where air can go, dust can go.