Well from all of your response I guess the problem is somewhere in the rear
heating core/valve/hoses. I appreciate all the responses.

I am curious though because the carpet is not wet under the rear seat,
around the core, or between the rear and middle seats. I know the rear
heater doesn't work so everything you all are saying immediately sounds like
it's the culprit. It just seems weird that the back would be dry. The wet
spot is in front of the middle seat and along the sliding door.

Thank you all and have a great Easter

Jeff