The toilets are American Standard and are 19 years old. Aside from the flappers, I am sure everything is original. It is black city in the tank from the decay of rubber parts. I need some advice on some brand names which hold up. I see that the big box hardware stores sell many different brands and types, ranging from in expensive to moderately expensive. The big box store is an easy way to go, but I wanted to get some comments on which parts/companies to avoid. Or maybe I should just avoid the big box stores and purchase the parts somewhere else. Any advice would be appreciated.