if you have the crank case just running to atmo it'll spray oil vapour all over the place and coat everything near by in oil when it breathes.

having a can means the oil is still caught in a can and the breather just puts out clean air. so it doesn't make a mess in the engine bay (and possibly cause a fire) and stink up the cabin by allowing oil vapour to pass through the cabin ventilation ducts.

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