Lost art of using Lead and not bondo

Any skill you can acquire is a good thing. The factory lead on my barracuda cracked. Plastic filler will flex.
I think the reason the factory used lead was because their seems were not completely welded and the lead would be better in that situation than the plastic filler. The lead will actually wick into the open seam and will bond better to the metal than plastic. The scientific label for the wicking is called capillary action and is an interesting phenomenon.
My barracuda was not welded at all on one windshield pillar seam. They tried but didn't get it tacked. That is all they try to do is tack weld the seam.
Modern cars for the most part do not have seams like the old days. If they do, it us a tiny little silicone bronze seam that is beautifully metal finished.

In my opinion, a better option would be weld or braze (silicone bronze is my choice) the joint then use the filler of your choice. Plastic filler, all-metal, kitty hair and lead are all acceptable choices when used correctly.