Factory seam sealer??

What did the factory use for seam sealing? on a 72 dart. Was sanding roof to epoxy seal for paint,when i got to the side near 1/4 panel a lot of body filler appeared. Dug it all out and found the seam(top to 1/4 panel) Guessing p/o filled it in .

Nope. That was very likely factory body filler. They all had it there.