I guess I'm on a different side here...

It's likely a $3 switch.

Fix it, and move on with your life.

Sure, the home owners knew and the Inspector should have caught it, but is it really worth potentially going to court? You could waste WEEKS on trying to push this through since you didn't do anything about it during the appropriate time in the contract. What's your time worth to you? Taking your time to chase this down with the realtors, the inspector, the previous homeowner, etc will all take time, especially if the previous home owner doesn't want to play ball.

The opportunity cost of WEEKS of effort is far greater than what it will cost to fix this.

Whatever, your choice to make!