A frequent repair for leaking toilets is a rusted out painted steel ring on a PVC or ABS closet flange. I make no secret of my like for stainless steel rings on PVC/ABS closet flanges they are far superior to painted steel or, worse yet all plastic closet flanges. I would urge every plumbing consumer to insist that the plumber use stainless steel ringed closet flanges if ABS or PVC pipes are being installed to a toilet. The extra couple of dollars it will cost is cheap compared to the cost of future repairs.
When you pull a toilet that has a leaking wax ring very often you find the closet flange had a painted steel ring and the ring is rusted badly enough that the closet bolts can no longer be secured in the ring. Until recently the repair options were either time consuming and expensive or, shoddy and inexpensive. On the expensive side it consisted of removing the old flange and installing a new one, this sometimes required a hole to be cut in the ceiling below to allow the plumber access to the toilet drain pipe. The inexpensive repair consisted of using aftermarket repair rings and spanner that although they would secure to the floor they did nothing to secure the plastic part of the flange and the strength of their ability to secure the closet bolts is doubtful at best.
Fortunately recently Oatey introduced the Moss Bay Replacement Flange P/N 42777 that is a strong stainless steel 2 piece ring that in addition to locking the closet bolts securely in place also grips onto the plastic part of the closet flange just like the original one piece ring that originally came on the flange. It is by far the best repair I have seen yet. The Moss Bay Replacement Flange is available at Lowes.
A Similar Product is made by Raven Products the 2 Piece Repair Flange for PVC/ABS Closet Flanges #BFR7900 and is sold at many plumbing supply houses.
To use the Moss Bay Replacement Flange or, the Raven Products 2 Piece Repair Flange the flooring must still be in good enough condition that the wood flooring can still solidly hold a screw that is screwed into it. Cut the old rusted steel ring off the plastic part of the closet flange without damaging the plastic flange. Remove all of the old ring from the locking groove in the plastic and the flooring. Remove two pieces of the new ring from the packaging. Do not use the closet bolts that come with this product. The only bad thing I can say about this product is that it comes supplied with ¼” zinc plated steel closet bolts. Instead use 5/16” solid brass closet bolts purchased separately. Place the two halves of the Moss Bay or, Raven Products Replacement Flange into the locking ring of the plastic section of the flange and put the closet bolts in place securing them with a nut and washer. The flange is now firmly locked onto the plastic section of the flange yet can still rotate. Rotate the flange until the closet bolts are square to the wall and then secure the ring to the floor using six #12 brass or stainless steel wood screws that are long enough to grip through all the layers of flooring.
Once this is complete your flange repair is better than the original and you are ready to reinstall the toilet with a new wax ring. Make sure that you use a new braided stainless steel closet supply, shim the toilet to prevent rocking if needed, and caulk around the base of the toilet with Phenoseal or Polyseamseal caulk, do not use a Silicone RTV based caulk as it can make the toilet very difficult to remove in the future if needed without damaging the toilet or, flooring. The job is now complete and ready for testing and use.