Is there a Cast Iron sleeve to put inside Cast Iron plumbing pipes to keep them from rusting?

I have a copper stack pipe coming down from upstairs washrooms leading into a cast iron drain line that ultimately goes through the basement and out to the septic tank. It looks as though the copper stack was simply run into the cast iron drain with some kind of sealant. At this point it appears...

I need to seal my horizontal pvc pipe toilet drain that inserts into a cast iron hub. Please help! Soil seal is not working!

I also have a similar problem. I have a second story bathroom and after a heavy rain there's water on the cabinets below that bathroom. The water is from outside the wood of the cabinet, so I can't tell if it's rain water or water from the sink or toilet (no shower in the upstairs bathroom)....

Just bought a house with damaged toilet. Existing plumbing is pvc toilet flange inserted into cast iron drain line. The flange is loose and needs to be refastened to the floor, subfloor condition permitting . How do I seal the pvc toilet flange to cast iron drain pipe to ensure no sewer gas leak?