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.