Plumbing Questions? Ask a Plumbing Expert.
There's a very good chance the lead has broke loose from the brass toilet flange. You will have to re-wipe the joint if that is the case. Only way to know is pull the toilet and examine the flange.
If you've never done this before, I suggest getting a lead sheet from the supply house and practicing. It can be tricky.
Anothe solution is cutting the entire lead 90 out and replacing with pvc.
A third (and less desirable) is to remove the brass flange, take a pvc flange and make sure it will fit snug into the lead. Take 100% silicon and thickly cover the sides of the flange. Puch it down into the lead and secure the flange. Wait 24hrs and reset the toilet.