You are absolutely right to black flag him until the car is inspected and safe as it can be.
You remind me of when my adoptive dad black flagged my dart off the road because of a corroded brake line when I was kid starting out with cars. Got it fixed and back on the road safely.
Thanks. He's 20 so I rarely put my foot down with him anymore. I figure he's grown. Dumb sometimes, but grown. Then we watch Roadkill and laugh at some of the dumb **** they do. IDK.