Actually, I never oil the inside just the outside, and as per my tech, a little is all you need not a lot.
FYI, I did have both my tranny axel seals changed on my subie tranny at the beginning of last season, as they were leaking, so it may have contributed to the K&N as it splashes all over the place and with the open engine to the ground it may be the reason I had to clean them more often while AC's are closed up.
I also had to clean the whole underneath the tranny lube was all over the place.
Update... I re-read the post and honestly I never heard of anyone coating the inside but who knows anything can happen.