It's a known fact in dirt bike racing that cleaning the filters with petrol ruins them.
It takes a while, but I've seen the effects first hand.

It makes the foam stiff and brittle and eats the little microscopic holes in the foam, leaving only larger holes which will let fine dust through.

I race motocross and enduro here in South Australia, which is probably one of the dustiest places on earth, so I go through HEAPS of air filters.

I clean mine in turps, then use Belray filter oil on my filters, (really thick) and Rock Oil filter oil on my filter skins, (much thinner).

I haven't played much with road bikes, (yet) but I reckon a thin filter oil would be the go as they don't get anywhere near as much dust as our dirt bikes.