Recharging a cone air filter

[devils_fuel]

wd40 evaperates off so is no good as it wont retain the dust once gone
id go with 3-in-1 spray oil for a cheap option
on 4 or two stoke stuff we used to oil the filters with the two stroke oil that we mixed in the tank
but the propper filter oil is not that expensive

So actual oil then, just thin viscosity?