Seam Sealer On Floors???

[horseballz]

68 Coupe, floors are virtually pristine except for the seam sealer which is dried out, cracked and crumbly/loose. What was this stuff originally and what/how should I use/do to address the issue? Not a concourse restoration but I want to properly seal and repaint, probably with POR-15 on the inside, before sound deadener and new carpet. Any and all thoughts, suggestions and opinions are welcome.
Thanx
Gene

 

[2+2GT]

Seam sealer is just that, 3M Seam Sealer. You can get this locally, or from most Mustang suppliers.