Leaky toilet drain

secutanudu

I have a toilet on the second floor bathroom that leaks down to the first floor occasionally. Usually just a few drops, but it obviously needs to be fixed. It happens when the toilet is flushed. The toilet is about 30 years old.

Here's what i have done so far. The bolts that hold the toilet to the floor were rusted and loose, allowing the toilet to rock/slide a little. I cut the bolts off, took off the toilet and replaced the wax ring with a new one (this ring also had a plastic flange attached to the underside). I then replaced the toilet and secured it to the floor with new bolts. The toilet is now very secure and does not move. I flushed it a few times, and it worked fine with no leaks, but eventually I saw water on the floor downstairs.

What could it be? Could it be the flange in the floor? Crack in the toilet?

If I need to buy a new toilet, I am fine with that. I just don't want to buy a new one and still have it leak. How do I pinpoint the problem? Thanks!

Edit...how do I know my wax ring made a good seal? Maybe I just installed it wrong?