ALL. I searched some to see if a write-up/post had been done on this topic. Didn't find one. Or I missed it. Here goes...
Have a 20+ year old Comanche? Cherokee? Smell Anti-Freeze in the cabin? :o Anti-Freeze as we know is highly toxic to the human body. Breathing it can cause eye & respiratory tract irritation.
My '00 XJ (250k mi) Heater Core has given up, but I don't have downtime to repair it just yet. I've made a temporary solution until I can swap out the entire box/assembly with new hardware.
Today (day 1) it is 65 F degrees Dec 1st, 2018 and no loss of coolant.
See photos for further details. I've done this on a Honda welding aluminum tubes together (I was bored), but this is by far easier and cheaper. I believe the Copper elbos we're $2.00 (US) each. The hose clamps are cheap too. Just solder the two Copper elbos together.