On the Kawasaki on the Lazer (25 Air cooled) I finally took and cut the top off the kawasaki filter and used it as a holder / top into a standard Kohler filter, extended the screw a bit and viola, I am filtering with a Standard Kohler filter that if I screw up and run out, I can run down to the farm store and pick one up.
I use a product called No-Toil oil on my Air filters, Motorcycles and prefilters for the mowers. Cleans up easy, non Haz and very, very very sticky. This is available through Motorcycle outlets / shops. You have to use their soap on their oil though.
It seems that I am forever behind on cleaning these things, try and clean prefilters once a week, new elements every couple of weeks to a month.
Al Bechard