hairline crack (with very slow drip) in cast-iron drain pipe.

We have an old cast iron drain pipe (maybe 100 years?) going from the main vent stack to the city drainage system.
I just noticed a damp spot underneath an area of the pipe and a corresponding light wetness along the bottomside of the pipe. Looking more closely, there was an irregular hairline crack in the pipe, extending perhaps 2-3 inches.
The discharge is (currently) clear and odorless and is truly minimal -- i.e. you can't even see drops dripping it is so slow.
So, short of replacing the pipe, what can i do to fix it?
Thanks
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Try to repair it with epoxy or JB Weld. It should repair it. Otherwise worse case, you can just replace that section of pipe with PVC and 2 no-hub clamps.
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JB Weld is OK. Make sure the crack is dry through and through first.
A higher quality fix would be to actually weld in a patch. It depends on how much peace of mind you want.
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I am not as worried about the current minimal leakage through the hairline crack (even duct tape seems to control that minimal level :).
Rather, I am worried about whether the crack itself will continue to spread and lead to a more catastrophic failure of the main drain pipe.
Would JB Weld be sufficient to prevent further destabilization of the pipe's integrity or is the hairline crack really just a symptom of a much more significant materials failure and a warning sign of an impending blowout?
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Could it be condensation?
What about using one of those no hub connectors as a patch. Would reqire cutting the coupling. For such a very small leak may do fine and is cheap and quick.

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Even better than the no hub connector, just get one of those rubber clamp-on patches. It is just a big rubber sheet, basically, with a bar on each end, that wraps around the pipe. The bars come together and are screwed tight.
-Kevin
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