This setup is drain lines in the first floor ceiling. The leak, to the left of the marking white tape in pic008(shown first), is activated by a second floor basin. A drip leak, not a stream. The ceiling was opened for another repair.

This work was certainly done prior to June, 1976.

The drip seemed to be coming from the green gunk in pic007. When I felt the gunk, it crumbled to the touch. The 2" cast iron pipe opening behind the green feels like crumbled garbage, but can't be seen currently.

How seal this 2" opening, which is at right angles to the floor/ceiling? The seeming offset pipe is actually somewhat below the leak opening.

You can't "seal" this... too far gone!

Only answer here is to cut out the bad piping material and replace it with new pipe/fittings.