I haven't had that issue, but if you know that you do, in this case you can buy the cups separately. After trying it out for a few weeks or months to make sure

I haven't had that issue, but if you know that you do, in this case you can buy the cups separately. After trying it out for a few weeks or months to make sure it's a keeper, just order another pair of cups? I got the impression that they've had phone parts in stock for a very long time, but of course that's relative to the average phone age and I don't know how many years you'd be expecting. In this case, though, if you already know what you'll need ahead of time... that's a cheap thing to just keep in a drawer. Can't go out of stock if you already have them and thereby double the other parts' longevity.