Where to get early A Body Heater Core?? or repair??

Looks like my heater core is starting to go south. Dumps fluid on floor only when heat is turned on. I'm pretty sure it is the original core. Are these worth repairing and if so, any recommendations?? If replacing is the way to go, again any recommendations on where to purchase. I've not had the pleasure of replacing one before but would like to do it only once....