The well water here is super hard, and anything immersed in it eventually becomes encrusted in calcium. It really does a number on the working bits of a toilet, as I long ago learned to my great inconvenience. Even when everybody isn’t freaking out about the plague du jour I can’t just hop in the car and head down to the local hardware any time I want. So if I know I’m going to have problems with a particular part, no matter how far in the future that trouble is likely to pop up, it really behooves me to have a Plan B handy.
When the toilet started leaking recently I was very pleased with myself that I could just amble out to the powershed, bring in my spares, and replace all the leaky bits, no problem. It wasn’t always so, but I do learn.