I was going to try leading one to see how it will holdup but haven't gotten around to it yet.However on one of the extra's I have for the 69 there was some bondo repair done.This car has been sitting in a scrap yard for the last 15 years and there was no sign that the extention had been fixed. Never noticed it until I cleaned the paint off of it. Don't know why lead will not work, just a bit touchy to use, take all safety measures , mask etc, if you try this .
Don