Not enough packing or not tamped in enough. Possibly cracked pipe.
Because you did it wrong.
Cut out the old piping and caulk a new cast iron bell and spigot with lead and oakum and test
Considering the waste inlet of the pipe of this pipe should be 4" possibly 3" you can buy an inside cast iron cutter .=You must measure the inside diameter and then buy /rent the one for the size you need THEN you can buy a new cast iron floor flange and use either a caulked joint (lead and oakum) or possibly a quick set type if the cast iron is no hub or standard weight=
Cut out the old piping and caulk a new cast iron bell and spigot with lead and oakum and test
Not the greatest idea, when packing in the oakum and then pouring the lead and caulking it the hub could split wide open Your new caulking job will last longer if you remove the old caulk and any of its debris and make sure the area is dry before adding new caulk. You can use an old screwdriver to remove the old.
A hole has developed in the spout or where it screws onto the pipe needs more Teflon tape or joint compound to seal the threads.
It could mean several things, but they all lead to a leak in your engine somewhere. Be it either old and cracked or broken seals to a hole in your oil pan. You should see a mechanic to determine the cause of the leak or you may end up with a bill of $5,000 for a new engine.
If the radiator was not fitted in properly or the pipes were not attached correctly, the radiator would leak.
buy a new one
If you have a new pressurised water system there is a possibility that the added water pressure could cause a leak.
look for the leak and repair it . I would do that before i thought about buying a new tranny.
To wipe a lead joint is an art that old time plumbers (when plumbers were plumbers) and not plumbers that know how to to put together plastic pipes with glue. My dad was one of those plumbers. Now i watched him wipe a lead joint a few times. I my self was never to good at it. I did it 2 times in my 30 years as a plumber so here i will tell you an alternate method my dad taught me. I believe you have an existing wipe joint leaking that connects with another type of pipe. 1st u cut out the wiped joint then take a 1" brass union end without nut slide over lead pipe than you flare lead over face of union. With other end of union connect to pipe you are connecting to then put the union together.What I do is remove the section of leaking lead pipe take a brass nipple Or copper tubing type "L" and wipe a joint using flemico # 1 solder or use a composition of 40 -60 as this gives a longer pasty range to work withUse a non acid type flux and use a ladle and wiping cloth . The key is to make sure both the lead and new pipe is toughly cleaned and fluxed
you should to repair it by : - soldering .....() - Brazing ........ () - or cut flare joint and start new flare joint .