So I have been running my Volvo and Honda air filters for 20,000 mile intervals. I NEVER open the air box to check on them in between changes. How do these look for 20,000 miles? The Honda is a 2012 V6 factory oiled filter so it looks much dirtier and the Volvo is a Napa Gold. Think 20,000 is ok? UOA has low dirt/silicon so I assume this is working well? I forgot to take pictures of the back side of the filters but both were really clean and looked new.