I had to replace mine also and mine cost me $75+!
The main reason for the replacement was that the spring came out and so did the keeper and the keeper ring broke for some reason. I fixed it last year when it came out but all I had to do is take a pair of needlenose pliers and grab the post that holds the gasket and twist it a little to get it to re-seat. I have found out by talking to others and the tech at the dealer-- that if you open a faucet in the unit you won't get that squirt in the face or on your pants (in a very embarrassing spot I may point out.
I'll try that next time but until then, I'll replace the whole city/tank fill unit and be a lot more careful next time!