I have an ABS toilet flange mounted into the concrete floor in my bathroom thats about 40 years old. Recently the flange was cracked when a new toilet was installed. The new toilet's bolts will not stay in the flange which causes the toilet to rock and eventually leak. I am attempting to Repair or replace the existing flange but can't seem to come up with the best solution. Attached is a photo of the existing flange. Additionally, there is no room between the concrete and existing flange to slide a retrofit peice underneath the cracked piece of ABS. If anyone can tell me what the best overall solution is to fix this problem I would greatly appreciate it. Thank all of you for your help.
There is a low profile two piece flange extension kit made of PVC. It has a thick and thin 1/2" and 1/4" extension with gasket and screws into your ABS. Depending on the level of your ABS you might have enough space but you need to check the height. It is called Quik-Fix Part # 274-100 from Plumb-Smart, imported by John L Schultz in Dorval Quebec.
Hope this helpps. Home Depot has it here.