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Prevents an engine fire/explosion in the event you have a major backfire. You really don't need to replace it, it is simply a plastic disc with lots of holes in it. The need is for it to be cleaned regularily. If it gets plugged you can build pressure in your engine and blow your rear main seal and leak lots of oil...expensive to fix. Check out Volvospeed.com for location. Cleaning it is as simple as spraying some carb cleaner through it until all the gunk is gone...then its as good as new. I usually do it every other oil change while waiting for the oil to drain. It's never been gunked up too bad.