The 1991 American Standard was not a good toilet.
I installed a few in 1992, the last of the 91's before they were gone.
One was installed in the homeowners powder bath downstairs.
They gave up on it and turned the downstairs bath into a storage room.
I would pull the A/S and put in something like the Toto Drake.
It doesn not have the same workings as your toilet.
Your neighbor knows less than you do.