I replaced the radiator heater core but when I took out the old one there were some ceramic or something washers that cover the in/out lines through the firewall, but when i took it out they crumbled to nothing so I put it back without them. I think I'm getting some fumes from the engine bay. What can I use to plug the excess hole after the fact?

Thanks
Rick
82 GMC Sierra Classic

 

Just squeeze some silicone around the inlet and outlet.

 

Any suggestion on specific product, does it need to be special heat rated silicone?

 

You don't need a high temp product as the temp won't be over ~200 degrees at the highest. Just go to the parts store and see what they have. Perma-Tex brand should have something available.