I switched to the K&N breathers early in the season and later noticed
oil residue on the driver's side. The breather was soaked. Ford Racing advised it was the K&N breathers and the driver's side was a bit lower to the cover therefore picking up more
oil mist. I think when you rev the car the K&N's leak. I love the way they look but will consider switching back to the FMS chrome jobbies or the baffled grommets mentioned above. BTW my valves covers are the baffled black ribbed ones.