RE: Challenger Rallye - 340 4BL
I agree that it's a freeze plug and you'll probably want to do them all.
Remember, to clean the surface well and don't just slap new ones in. They don't just stay in there by themselves. You'll need to coat the mated suface with Permatex Form-a-gasket. Tell the guys at the parts counter what you are doing and they should point you to the right tube.
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