Cast Iron Toilet Flange

Can I use oakum and lead wool to put the flange instead of pouring lead

Do you have access to the bottom of the flanege - say - access to the floor below?

I can not imagine why you would not even try to relead flange cast iron is a really easy to replace. They make a PVC replacement flange that fits inside the pipe four inch cast as the flange is now, and an Allen wrench tightening 3 screws that take a tapered ring up to broadcast a gasket rubber seal inside leaks. Takes about five minutes to install, and not very expensive.

yep works the same,

neoprene gasket works better.