Yes, there is a rubber diaphragm in there and it's extremely odd that this would fail on an '07 model car with only 46k miles on it.
Everyone has their own way of doing things, but as a mechanic I've devoted a bit of my time for free and after hours to try and determine why something failed. Not knowing irritates me to no end so you might ask your mechanic if he can determine what caused this premature failure.
You might consider contacting the Toyota regional office and asking politely if they could consider doing a Good Will warranty on this. The worst that can happen is that they will say no. There's at least a possibility they could step in and reimburse you completely or partially on this.
(And please excuse my double post. The PC locked up and I assumed the first post had disappeared into outer space.)