I have the K&N drop ins also and have no problems with gunking up the MAF. As others have said, just be careful when re-oiling the filters. I always clean and re-oil them out of the box, since they tend to come to oiled for my like. Buy the K&N recharge oil kit, but get the one with the spray oil and not the liquid oil. Much easier to apply evenly. Even if you think you apply too much, can always clean and re-oil. You want the filter a light pink and not dark red. Also, I like to place them on paper towels after, and that helps draw out the excess. When I stop seeing red on the paper towel (if was any to begin with), then I know it is good.
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