Pop-up Stopper IRL

I came home the other day, and my bathroom sink wasn't draining. I found that the plunger, sometimes a.k.a., but not to be confused with the Internet version of
pop up stopper, was recessed in the valve seat, but the actuator would not move it.

Prying it out of the hole, I find that the plastic stem was broken off. Nobody wanted to fess up how this happened. We're in the middle of renovating our other bathroom, so needless to say, I was a little upset. The kids promptly blamed it on Grandma, stating that she was trying to get some gunck and hair out. She denies it, but I found a hanger with a hairball in the trash, and telltale scratch marks on the stainless steel, mirror-finish of the Kohler cover. If you look really close at the white paper, you can see the reflection of the scratches on it.

At the second hardware store, the guy tells me that my sink is old, and I need the entire assembly ($20) rather than the stopper ($5). We replaced the sink less than four years ago when we moved into the house, so you know he's full of shit. I guess I didn't have the latest 2005 model (or is it now the 2006 model year for sinks?). After a trip to third hardware store, I find a suitable replacement.