The cheapest 30 weight oil you can find will work just fine. The only purpose for having oil in the filter is to trap the dust and other heavy particles in the air as it makes a 180 degree turn as it passes through the air cleaner. Any oil will work, even hydraulic fluid, transmission fluid, or 90-weight gear lube. There doesn't need to be enough oil in the assembly for it to migrate into the packing of the upper section, although some people like to mist some kind of lightweight aerosol like WD-40 or something similar into the woven part of the filter.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!