From the image I am submitting, can I get opinions on what is going on with this waste pipe? It looks like a crack that's
seeping. A plumber, giving an estimate on another job, said it was nothing but a leak from above. It doesn't appear like nothing to us. Nor does it appear there is any leak above it. It also is more recent occurrence as this was not here a year ago when the home was purchased. The home is 92 years old. Thank you so much.

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If it doesn't appear to be actively leaking, I wouldn't mess with it at this point. When you start messing with the lead going to the toilet, you will have to pull the stool and replace the flange and continue down to the stack. Since this isn't under pressure, or constant use, you could attempt to clean the pipe down the crack at least a full inch on either side, then use epoxy with a backer material to help push the epoxy into the joint, and keep it from running out everywhere.