'93 Plymouth heater core.

If you are into pain, tight quarters, floorboard humps and are proficient at dismantling dashboards, and are fond of coolant, small screws, clips and plastic trim, and have standard tools as well as a small socket set, and have about 6 hours to spare, (unless it's a rear heater core problem which is a bit less consuming), you can find a repair manual under $20.00 to walk (or should I say contort) your way through the procedure. It may be possible to acquire the step by step from your local library as well.
Personally, I quit doing heater cores a few years ago. I now have a younger, smaller framed tech perform these tasks, unless it's a nice vintage vehicle with a mounting plate on the firewall and secured with only a few bolts.
Ahhh. They don't make access like that anymore.

Aacplus. Thanx for the feedback. Nope, it isn't on the firewall. It is sorta behind the radio. Guess I better count of spending a day dong it. It isn't fogging the windshield or leaking inside or out but sure can smell it. Thanx again.

Jack