I second Redwood's advice for two reasons:
1. The rubber diaphragms are available separately for the 400A (as well as the preceding 200A).
2. Most people aren't aware of this, but you can replace the top portion of the 400A almost as easily as you could with the old 200A. Just slide the retaining collar up, and give the top part of the 400A a good strong yank and it'll separate from the bottom portion that will remain in the tank. (obviously shut the water off to the fill valve before yanking the top off or you'll have a water geiser)
But, the advantage here would be that you can have a "spare" top portion that you can push onto the bottom portion of any toilet that's leaking, and then just clean the rubber diaphragm in the top portion you pulled off so that it's ready to go into service whenever the next toilet leaks. That is, you can have a spare "top portion" that you can replace within 60 seconds, and then clean the rubber diaphram in the top portion you pulled off in your spare time at a more convenient location, like a kitchen table.
StanS: You should be aware that all toilet fill valves (that I know of) work by using the water pressure itself to shut off the flow of water. It's the same system that's used on washing machine water mixing valves, and it's very reliable. However, it's also very sensitive to dirt getting into the area where the rubber diaphragm is. So, if it wuz me, I would see if I could fit a hose washer with an integral filtration screen, the same kind as is used on the water supply hoses to washing machines, into the connection at the bottom of your toilet's fill valve. I'd try to get the hose washers with the very fine mesh stainless steel screens. You should be able to find these at any appliance parts store.
Hose washers with the coarser brass wire screens are also available, but I'd opt for the finer mesh stainless steel wire screens in this case.