A guy at a Cars and Coffee in Sacramento told me my valve lash was too loose, and he was right
I was parked next to a '69 Datsun 510 last month and the owner leaned over my fender after I shut the hood. He listened to my engine idle for maybe 15 seconds and said, "That tick isn't an exhaust leak, pull your valve cover." I blew him off at first because I had convinced myself it was a cracked manifold gasket. Two weeks later I finally checked the lash and three rockers were way out of spec, one by almost .006 inches. Has anyone else had a total stranger diagnose their car by ear like that?
Oh man, that reminds me of the time a random guy at a gas station told me my belts were about to go just from hearing my truck start up. I laughed it off and then two days later one snapped on the freeway. Some people just have ears like a mechanic's stethoscope, it's honestly a little creepy.