The old 405 estate still loses a little water ... somewhere ... maybe a cup every five hundred miles or so. The heater and demister also seem to mist the inside windows a bit. I can never find a leak and the heater matrix was renewed not that long ago. So I wonder ....
Does the mister mystery accord with those two little O-rings in the joint to the heater matrix not being as good as they should be, or compressed as tight as they should be? It is time to crack open this joint again the slop some mastic gunge around the O-rings and change the screw for a torx or hex-head bolt?
Cheers,