68 Dart Heater Core Replacement

You can use many things for that firewall seal. I would cut some black foam rubber to fit on the inside, over the tubes. I have a HF hole punch set I use all the time for such things. You could also seal it from the engine side, using stuff in the Home Depot door/window seals, but might look ugly. The water cudacrazy67 is talking about is rainwater that drips down from the cowl.