I have gone through exactly what you are describing. I refuse to run K&N's anymore, because in my experience they always pass a little bit of silt. Didn't seem to matter how well I oiled them either. If you take that K&N and look towards a bright light through it, you'll see lots of pinpoints of light...they really are quite porous. I don't trust them, and will only use a good 2-stage foam filter. These clean the incoming air a LOT better, and don't seem to detract from the power...at least it's worth it to me whatever small tradeoff might exist. Why dust your motor when you don't have to?
Hope that helps.