You can replace them. They are most likely cheap builder grade toilets, you get what you pay for.
My daughter had them in her new home, long story.
The weekend she move in I offered to take them to the dump and replace them with Toto toilets.
She was a bit bugged with me, after all, it was a new home with new plumbing.
They plugged up all three Mansfield toilets the first weekend. When I would go over there, there was a plunger by every toilet.
Two Christmass ago, she asked if I would still replace the darn things.
I did, and she hasn't needed the plungers since.