Is it actually old and corroded?
I gave my car to my garage before putting it through the MOT just to give it a check over as was worried about a couple of things it might fail on and they picked up that there was some rust on the copper lines. They said however that it was just surface rust but would have to fail it because its 'rusty'.
He basically said give the rust a light rub down with some wet and dry or something and grease it up.
If they are properly old and corroded then yeah I guess it's replacement time
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