1966 Dart GT-it begins

This the response I got from RestoRick:


That looks more like the tar based sealer used on interior seams.
(Later cars used a brushable sealer that was a tan color.)

For the black type I use Blackjack Neoprene Flashing Cement.
It dries to a rubbery consistency. I get it at Menards, if you have access
to them.
Amazon.com: Black Jack 10109066 10OZ 10 Oz Super Flash-Neoprene Rubber Flashing Cement : Industrial & Scientific