Well, this may be pre mature but  fix seems to be working at least after one test drive.

I replaced my rear heater core that had warped by the heater valve.  I then replaced the o Ring threee times.  Third time a capable sighted friend did it. 

Always seeped coolant. 

I had decided to have a friend use permanent tex or other gasket stuff but just for a last ditch effort I took about 10 inches of rescue tape and pulled it around the seam.  I was not sure I was even able to cover it all at one spot.  Still it felt amazingly like a nice seal when done.

So, a pretty significant test run later.  That means we did errands in the van, I checked and for the first time since I started to work on the problem there was no seepage detectable.  

        Time will tell if it will hold up and if it is really working.  But nice to finally have one trip without coolant seep on the rear heater valve. 

Rescue tape has been reportedly folks on this list as lasting a pretty long time.  I think one person reported forgetting to replace a patched coolant hose for about 70 K.

Now to find the source of the coolant smell outside the van.

Eric Caron 
85 and 84 Westfalia