I noticed on the stock filter the wire cage is sloppy and seems to separate the foam filter from the plastic housing a little bit near the ends. This could be a path for dust to pass by without being filtered. I used a little swipe of grease on each end of the element to prevent this. On my first service I saw a little dust build up in the intake past the filter that made me look for a the problem....should be good to go now.
Mark