Help diagnosing bathroom faucet leak

Hi - I'm trying to figure out what's leaking on my bathroom faucet.

- Nothing leaks when the faucet is in the off position.
- When the faucet is turned on, from underneath the sink, water starts leaking a lot down through the hole in the sink where the lift rod runs through.
- I don't know much about plumbing at all, but I was able to take the handle off of the faucet and inspect it. There didn't seem to be any visibly bad seals around the cartridge.
- My house was built in in 2006, and this is the original American Standard faucet.
- I'd rather not spend several hundred dollars to call someone out if this could be a quick fix.
- Any thoughts? Pictures attached. Thanks!

I guess I figured it out on my own. Spent an hour and it was the dang areator. It wasn't screwed on very tight, and the washer on it needed a bit of cleaning.

Saved me the trouble of pointing out that it was likely the areator leaking back through the spout.