RC tech sell air filter cleaning solution (which smells and feels suspiciously like turps), which in my opinion is magic..
I've never seen anything pull so much fine crud out of a filter.. it even pulls the finest of dust out. The finest of the silt left in the bottom of the cleaning bucket, when dried out is as fine and smooth as graphite powder nearly.. It even collected fine crud out of a couple of filters that were as clean as soapy water would get them.
We apparently have some of the hardest dusts to filter coz they're so fine here in Australia, I'm told by an automotive engineer. Thats one of the reasons why we have to change things like air cleaners etc etc to get imported cars registered over here.
I'm not trying to sell this product, I just think it is magic stuff. Their filter oil is pretty good too. I was using K & N red filter oil, but it seems to clog the element, and the dirt doesnt stick to it as well as the RC Tech stuff I reckon. Since changing to RC Tech from K & N, my inner filter has not had any noticable dust reaching it, whereas it would most of the time with the K & N stuff.
I trust this stuff enough to not to buy new elements. I have a few genuine x-ray filter assy's which I just swap between races and clean when I get home (I'm not happy with using aftermarket filters on something like an X-ray.. its like putting aftermarket parts on a Rolls Royce - You'd be degrading the rest of the car by doing it!)
I've started using the RC Tech stuff on my Pod filter on my real car instead of the K & N stuff..
Oh yeah, its got a blue dye in it (I think turps has to be dyed blue here in Australia nowadays coz there are too many dickheads in certain areas of Australia out there that drink it!?!) so it dyes your white elements blue