1964 C10 Firewall grommet for tail light harness?

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I have been gathering parts for upgrading the main wiring harness and just purchased a firewall grommet kit. Is there a grommet available for the tail light harness at the firewall?? I have most of the others with a kit from Classic and am unable to find one available at any of the part vendors.

The current tail light plug is poorly sealed with a bunch of RTV and trying to find a better solution and or ideas.

Thanks!!