removed my vinyl top and found this

Preparing the '72 scamp for paint. removed the vinyl top knowing there was some rust bubbles under the vinyl. Found this, which I assume is the factory seam between the roof and the rear quarter panel. It had what appears to be 41-year-old plastic filler. Was this factory? Wasn't there a time they used lead to fill this seam? I'm going to paint the top and have a perfect OEM headliner already in place, should I reuse filler or take the trouble to remove the headliner and weld the seam before paint?