Have no idea why anyone would put filters on the hose endings unless your car shoots a **** ton of blow by oil and sprays oil everytime you let off the throttle under the mildest conditions to WOT....And if that IS happening, you would DEF need to check your PCV valve/system since its not suppose to have really any oil in there in the first place.
IMHO this is something that can actually help keep your intercooler, intake manifold, chargepipe ect.. nice and clean since the small amounts of oil residue that most NORMAL N54 motors produce just slowly drip after it being built up onto the belly pan under the motor. I would much rather have it there than oil going into my intercooler or intake manifold when its not suppose to.
On the other hand, this should just be a temporary fix until you can afford a Tial BOV setup or HKS BOV setup ect.. Yes the stock diverter valves do the same thing a BOV does but wasn't designed for it nor was it designed to handle almost double the horsepower from the factory yet some people making over 500rwhp still have the stock DV setup and aren't complaining about them leaking ect....
Instead of putting filters on the endings of the piping, you should save the money and invest in a BMS OCC. By far best one on the market IMHO since its literally as simple as reading the directions on how to do it. Still, I would FIRST replace your PCV valve with a RB PCV valve which is way more durable under higher power outputs and hold up 10X better than the factory unit....Plus its extremely cheap...infact its cheaper than the stock ones lol...just checked really quick. You can order it from Rob directly, or go to burgertuning.com and Terry sells them for the same price on his site and they look to be in stock.
By the way, it is EXTREMELY easy to install/uninstall your PCV valve once you have your cowl and cabin air filter off so I def suggest you ordering one first, then the BMS OCC, and then a proper BOV setup to handle bigger power numbers than stock 8psi of boost that the car in stock form produces
sorry for the long response but just my 2cents on the subject. And a BOV sounds 10x better with the car being a manual 6-speed,******* ********* back exhaust (delete secondary cats=less backpressure) and your choice of muffler. I personally have tried just about every setup there is but nothing is better than 3"******* *********, secondary *** delete/resonator delete, to a BMW Performance exhaust! You can literally hear your turbos whistling which sounds so damn good
