There is a great article on air filters and maintenance of them in the latest TDR issue (#47, Pg 82) written by Joseph Donnelly. It gets into the very subject of using different oils on these filters. What was found was that the "AFE oil is finer, wicks better and doesn't cake on MAP sensors in the manifold. " This is just a small out-take that I wrote from memory but the article hits a little more on the subject of maintenance. It's a very well written piece and I highly suggest all with high flow filters read it for the info. It's enough for me to NOT use the K&N stuff on my AFE.
Bert