I looked at an FL-400s yesterday. Not only was the price double what I paid a few years ago ($8.44 vs $3.99) it did have the louvers just like you said. At least they were supposed to be louvers, they were not good and I would not have bought that filter.Every new Purolator (and Purolator built, like Motorcraft filters) I've looked at in the stores all have louvers. And some not very well formed IMO. Varies between them, no consistency. Inspect well before buying.