Best Grease Dielectric? For Firewall Connectors

Corrosion preventative compound works great if you can find it.

Product Description​

A highly effective water displacing, non-staining, non-hardening, non-conductive corrosion preventative. Concentrated solution is suitable for avionic equipment and general purpose work. The lower viscosity solution is for use with electronic components. Use on any metal surface such as hinges, machinery, electronic components and all types of metallic sliding parts. MIL-C-81309.