This forum helped me through the same problem and it came out great! I am not a plumber but have done lots of DIY projects and have experience with soldering. My toilet in my 1997 home was wobbly so I took it off and was surprised to find a lead bend. In fact it was pretty badly damaged and not even bolted to the floor! Someone had attempted to solder it but clearly did a bad job. I was very worried that I'd have to replace the lead bend which is encased in the concrete foundation.
I bought a deep brass flange online, roughed up the inside surface and then pre-soldered it with 60/40 solder. Then I cleaned up the lead bend and carefully tapped it back into shape so the flange would fit. I had to pour some new concrete patch to raise up the flange so it sat on the level of the finished floor. Then I drilled 4 holes to screw in 1/4 inch Tapcons and anchored it down. Unfortunately one of the tap on screws broke off in the hole but at least I got 3 in there.
Once the flange was anchored I applied flux to the outside of the lead bend and tapped it out against the flange. To solder I used a propane torch and was really careful to heat the flange just barely to the point where the solder would melt and suck into the joint. I added solder as I went, even though I had pre-applied solder. I wanted to make sure the gap was completely filled.
It really wasn't too difficult and I feel really good about the end product. It seems like it will last longer than the house now! Thanks everyone.
