Rear heat not working town and country crystler 2009

Rear heat not working in 2009 limited Town and Country.  We originally took it to the
dealership because our heat wasn't working and we noticed a liquid all over engine.  Van
even overheated on the way to dealership. We  paid extra to have a lifetime warranty
when we bought the car.  Car has around 50k miles.  Dealership said a hose leaked and
we had no liquid. T hey replaced the hose and they called us to pick it up.  Upon picking
it up we noticed a note on the paper stating a foreign substance was found in the system.  
We didn't think anything of it and drove on our way, everything was covered by our
insurance.  While driving the heat worked great up front but the rear system that has its
own controls only blew cold air, even when the heat was on high.  We made and
appointment and brought it back.  The service manager at the dealership said someone
putt stopleak in the system which caused the entire system to be blocked.  They stated it
voided the warranty and it would not be covered.  After arguing with them for hours and
explaining 1) we never brought our van to any place but two dealerships, and jiffy lube for
a transmission flush and 2) this was the first leak our car has ever had so why would
anyone put it in.  We had the car in their shop within 10 minutes of finding out our system
was leaking.  So finally they decided to take a look, the said the did a flush, cleaned the
hoses manually and then replaced the heating element (I think that's what they called it).  
They called today and said that after all that it worked for a couple of minutes and the.
Stopped because the stop leak is all throughout the system and in the radiator and
everywhere so it clogged the rear system up again, even though air is coming out.  I
asked if the front was still working and they said yes but it is just a matter of time until it
breaks.  And when it does they will no longer do work on this car under warranty because
the stop leak will cause all kinds of problems.  I'm at a loss.  I can't imagine who would
have put it in if it in there. They said it is clumpy and a tar like substance and only stop
leak would look like that.  It is so frustrating because how do I know it is that and how do I
know they didn't out it in when I first brought it there.  Im at a loss.  Please help.