Sealer in firewall pal nuts?

[runnin74]

I'm working on the electrical bulkhead and fuse block on my 74 and was wondering what the black sticky insert is in the pal nuts used on the firewall side of the bulkhead disconnect? What does everyone use to replace it? I presume it is there to seal the screw hole in the firewall. See pic.

 

[hemi#1]

there is a rope calk it's butyl calk I've found it my local auto paint supplier or at some swap meets