Finally got around to checking inside the air box after running 9 hours to date. There is definitely some dust on top of the post filter as well as a layer of 'film' inside the lid of the air box. Not nearly as bad as the pictures posted by the OP but yeah this is supposed to be the 'clean' part of the air box. Most of my trail riding has been as the sweep rider so I was in extremely dusty conditions. I went ahead and put a bead of grease around the top edges of the plastic tray that the post filter sits on. Just used enough to fill the gap between the plastic tray and the actual air box body. I feel that will prevent any dust from working around the edges of the dust filter. Also, when I first installed the post filter it was so saturated with oil it was dripping. So I wrung out some of the oil before I installed it but it still made a heck of a mess inside the air box. Now that's not really a problem and I'll get it cleaned up eventually but they sure must use some crappy foam filter oil on these things. I'll put some of my Bel Ray on it next time and I doubt it will make a mess again. I think they use UNI oil and it just doesn't seem 'tacky' enough to hold itself in the filter. Post filter is definitely a good idea though and I won't be running without it. This thing can save your motor but I think it needs a little help such as my grease bead.