TL;DR: An older shower faucet stem is leaking, and the shower won't turn off all the way. What can we do to get it to turn off?
Videos of the issue: https://drive.google.com/open?id=14tL63ksW7176nh5M79gP8cdsryuL6pJO
Here's the story: The house was built in 1965, so original hardware. We've...