I ran a AirHog by Fram for a couple years, cleaned and oiled it just fine, since I used a K&N on my FJ40 LandCruiser years ago), but I swapped this one out for paper when I was getting sensor codes - there seems to be some ideas that the oil from the filter can get drawn in, so I wanted to remove that possibility. However I've seen some tests that debunked that idea. I think my O2 sensor was just time for replacement and the MAF was fine. I think Scotty K. even talked bad about the oiled filters, but does anyone have first hand experience? I never over-oiled and now have spray and will probably go back to it.