When I had my 70 Challenger in the late 70's, my lead seam started to crack right at the corner of the quarter window and down where the quarter meets the rocker panel. Since my car was originally a 318 3 speed and I converted it to a pumped up 440, I accepted it at the time. I was hard on the pedal and the body twisted a lot. When I did the body work on it, I did use all metal and didn't have any issues with it for the 2 years I kept it. On the Cuda I have now, I welded the seam all the way across for safe measures since I could. I didn't lead it though. This site is great for the fact you can get multiple opinions. Pick and choose what you feel comfortable with. In the end, we are all car guys.