i use motor saver and very well oiled using the thick AE oil.
after race day, my inner filter shows a little brown mark... i suppose dirt does get thru, but i have done everything to try stop it, i would have to change air filter every 2 heats to prevent it... no filter system is 100% effective and so long as it let in just very minimal amounts then it should be ok... oh my engines last well over 6 gallon mark...