I'm replacing the heater core on my 1966 Olds Ninety Eight. It had a felt-like insulation between it and the firewall, that's all soaked in coolant, and a bit torn up now. What do you use as a replacement? Can't seem to find the same thing from any of my usual sources (USA Parts Supply, Fusick, Year One)???

 

Have you tried your local parts house? If you can't locate one, you can use ribbon caulk to create your own gasket.

 

Tried Piston Ring and a performance shop, both said part is discontinued. That self-made gasket stuff is so different from what was originally there, I'm just not sure. It was a thick felt-like pad that covered almost the entire heater box. 99% sure it was original. I see Year One offers a "heater to firewall seal" for a 1960s Cutlass, described as a "white rope caulk sealant" that comes in a 30-foot roll. That sound usable, or is there something else out there I haven't been able to find?

 

Yes, that is the stuff I was referring to.