Mopar lead sled

Years ago, the vinyl top on my dart bubbled out so I pulled the top and it's been rusting ever since. It had body filter in the c pillar seams that fell out like methhead teeth. Should it have been lead? When did Chrysler switch from lead? My '75 has no top and shows no issues in the seam.

Is lead or body filler the recommended material to refill these seams with?

I'm NOT a body guy, so many thanks in advance!