Confirm Pop-Up Assembly Damage

What happens here

With the pivot rod removed, carefully examine its end, particularly the small ball (pivot ball) and the part that extends into the drain pipe. This extension is what normally connects to the stopper's bar. In this particular case, the video clearly shows that the end of the pivot rod is severely corroded, and the portion that would engage with the stopper's bar has completely rusted away and broken off. This confirms the visual inspection from Step 1, explaining why the sink stopper cannot be reinstalled or held in place.

Goal: Verify the specific failure point within the pop-up assembly.