My in-laws have a somewhat similar issue, except on their supply line. Noticed wet walls/ceiling and had no choice but to open the walls to replace a section of pipe. Problem is they don't know if it goes beyond that. There's evidence of corrosion on the pipes further down the wall, but was that just run off from the leak above, or another leak?Right now the only visible evidence of a crack is on a visible section of pipe that runs from the kitchen, over top of the washer, then over and behind drywall. The crack is on a jointed piece of cast iron where it comes out from the kitchen and over the to wall. We never really addressed the question of can the jointed piece be replaced because we went from worrying about the cracked piece to talking about tearing out walls very quickly. So I don't really know if the visible crack can be replaced without tearing up the wall.
Wouldn't he have to tear open the walls to replace the pipe anyway?
The only evidence of water damage is a hole in the subfloor, but the hole wasn't moist (twss) and I don't see any evidence of water anywhere else.
They're not taking any chances and just going to have the entire pipe replaced instead of just that section. You should probably do the same, but YMMV.