Genuine Oil Filter.
There are so many different recommendations for oil.
Here's a bit of bed time reading: http://www.perth-wrx.com/vb/showthre...ecommendations

Is your car modified? Do you take it to the track?

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MY99 WRX (Sold)
MY06 WRX 241hp 430nm atw (Sold)
MY09 BMW 135i 247kw atw (Current)