I'm having some issues with my toilet flange. I have a cast iron flange attached to a 4" ABS pipe. The flange sits level to the tile floor. However, the tile floor is not level so the toilet rocks. The issues I'm having are 1)the old flange is broken in 2 spots and bolts do not sit properly 2) flange is misaligned so toilet sits crooked. 3) although the flange is level to the floor, it dips down a little in the back on one side. Is there any way to repair these issues without having to remove the old flange? Is there anyway to install a new flange over the existing?