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Looking at it, noticing the contact marks towards the middle of the piece and looking at the shape of the whole thing...could it be some sort of pressure controlling pin? Something that opens, closes (moves in and out)? (My luck, this is some VEEEERY important piece which prevents my car from exploding after 30 minutes drive-time and since I don't drive more than 30 minutes daily I have barely avoided a horrible death...over and over).