I have used a Pro strength Orange Cleaner for tough to do jobs. I got it at Lowes in a gallon jug, but it probably comes in smaller sizes too. I use the Harley Screaming Eagle air cleaner. First, I pour some orange cleaner in a small pan, ,maybe 1/2" or so. Next, I roll the air cleaner in the solution, maybe 3 or 4 complete rounds. Let it set for ten minutes or so, while that orange stuff cuts the oil and grease. Lastly I take it outside and turn the hose on it from the inside pointing outward, not a high pressure stream, but some, enough to push the softened gunk out of the filter. Now, let the filter sit overnight to dry. Don't blast it with the air hose. Next day, it is nice and clean and ready to install. I have done this with my current filter at each fluid change. After five cleanings, it still looks new. What really screws one up is when you overfill the crankcase and it pukes the air filter full of oil. That will make it extra hard to breath and over time the oil drys out and turns harder than rooster lips.