John, I worked at a Buick dealer in the late 60's, I worked in the parts department, so I was always in and out of the Body Shop.
I can't tell you how many nearly new cars came in for repairs that had been in an accident, and when the guys at the body shop started sanding down the panels they would run into bondo.
I don't remember ever seeing lead. I'm not saying they didn't use it, but I sure as heck never saw it.