Check the toilet report link below, it's made for this question.
1996 was not a good year for toilets.
If you replace them with the new highly rated ones, it should help a lot.
Most people with good toilets forget where they put the plunger after a while. And forget about floods anymore.
I do wind up selling a lot of the Toto brand toilets, they work, and the quality control is fantastic.
You should be able to find them on the mainland near where you live.