The advice you got is excellent. Personally, I've run into trouble
when I mount the new flange on top of the tile. There used to be enough
room to do this and not have a problem with the toilet sitting flat on
the floor, but I think they're making them without that tolerance lately.
Fluidmaster makes a very thin steel flange that works on top of the
tile, but you need enough lead on the closet bend to hammer a flare on
the inside of the flange. Now I know this would get me into trouble at
Bob W.'s shop, but I don't bother to solder the lead to the collar.
Since the closet bend in is a concrete slab, the wax ring would make an
What I've also used is a PVC repair collar that reaches several
inches into the closet bend. It comes with a big "O" Ring that makes
the seal. If you use this, you'll need to chip the tile and get the
collar down to the cement level.
And Bob, W., I promise that if I worked for you, you'd love me as a
person, but probably I'd eventually drive you nuts.