I have a CP-E CAI on my MS3. It comes with a large, conical dry element that ends up behind the liner in the driver side wheel well. I have used the optional filter "sock" since new. Since this filter is now in a real PITA location, I don't inspect it very often. I've got about 20,000 miles on it and everything stills runs just fine. It's hard to imagine that filter getting very dirty with the sock over it but I'm wondering if those with experience with this setup might offer opinions/guidance on replacement intervals.