Wall Mount Toilet Leaking

I have 2 American Standard Glenwall wall-mount toilets mounted back-to-back in two bathrooms. I also have a leak that seems to occur when they are flushed. When I removed them I saw that they were installed with wax rings, which I understand is not proper. I bought two neoprene gaskets, put them into each toilet outlet, and put the toilets back and tightened but still have a leak. Do I need to use any kind of sealer and/or epoxy? Or glue the gaskets to the carrier waste horn instead of putting into the toilet outlet? I would like to eliminate ring/gasket problems before cutting into the walls and ceiling to look at the pipes and carrier. I did see some directions at https://terrylove.com/pdf/glenwall_install.pdf but didn't understand the part about the gaskets. Thanks in advance for your help.

The Neoprene washers come with adhesive. We coat both sides.