Run that K&N for a while (with or without Outerwear) and you will begin to see some blemishing on the OD of your piston!  That's WEAR.  And when you look inside your reed block, you'll start to see some fine dust. 

K&N is made for flow...that's it.  They beat the "ping-pong-ball flow test" with flying colors, but they don't stop dirt & dust (not efficient).  If you met the people from K&N, you'd know they were about making filters that FLOW and making gos of money to pay for their motorhead hobbies.  Nice people, though!

On the dunes and trail, use the dual-layer UNI and wash it regularly.