What I'd like to try is getting a Grimmspeed AOS and getting a RS Liberty Alloy Oil filler neck. Cut off the head of the RS alloy oil filler neck 1cm below the thread for the oil cap and then weld that to a 1 or 2L alloy tank. Then screw the Grimmspeed AOS onto the newly completed tank and mount it somewhere. Then you can either run the clean pipe from the Grimmspeed AOS back to the intake or to a filtered breather.

I never liked how the Grimmspeed AOS looked screwed directly to the OEM oil filler neck. it just looks messy and comes too close to hitting the bonnet.

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RS Liberty - Because WRX's are only good for parts...