Well, quick post to update what I found causing the earlier mentioned coolant leak in the heating circuit.
It appears that a rather tight bend in the heater hose turned into a fold at some point (though still flowing water) and the brass-tube inserted inside (where connected up to the 12V Aux Pump) sawed through the hose and produced a TINY LITTLE CUT.
A fairly easy repair all in all. Drop the muffler, cut off the bad section of hose, re-route and push back onto the pipe and clamp down. Appeared to be okay for this last trip, but a LOT of extra zip-ties helped the situation.
I can still taste the coolant….