One of these ducts had a very slow drip of water. I was able to make out a very fine hairline crack and put some tape over it. The lead seems to have stopped so I took the tape off and now can't even see the crack. Diagnosis?

A picture would make it easy. Are these items made of copper?

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A picture would make it easy. Are these items made out of copper?

No, they're silver metal. This happened yesterday, but today I see nothing. I pulled off the tape and it's dry. Can't understand it because I'm sure there was nothing dripping from the ceiling above the duct. We just had 3 feet of snow over the weekend and maybe that had something to do with some sort of condensation? I really know nothing about these things.