No slots for toilet bolts just oval spaces on the sides of the flange. Invariably the bolts slip out and the toilet rocks. The house is probably 80yrs old and the cast iron flange is original. Any ideas? Thanks.
Go to a plumbing supply house and get one of these
You will need to cut the old flange off to install this. If it is leaded on, dig out the lead to remove the flange. When you tighten the 3 bolts in the picture, it secures it to the old pipe.