My experience is like Mark's- lead at the join of the roof to the quarter panel. They'd go light when the cars had a vinyl top, too. As for abuse of vehicles at the plant, You wouldn't believe the drag racing between the cars out in the "back 40". I know a guy who started a '72 350 Z-28 engine while it was on the chain, using a can of gas and a battery. He wound it out until the exhaust manifolds were red hot and then disconnected the battery. It hung there, dieseling, for awhile. I wonder if the dealer had to replace the engine
before selling the car that went in.
He was a real jackass.