Hello and Happy Spring to all!

I'm wondering why my '91's rear heater leaks coolant only when heater is
'off' - yes off, lever to rear, no heat?

I'm not sure what exactly is leaking - core or valve or O'ring.   I don't
see or feel any sign of leak from the lines, bleeder or valve or anywhere I
can reach to feel on the housing.  Just underneath the whole thing.  I
haven't had the black plastic cover off - don't think that is something I
want to tackle myself.  Can the valve or O'ring leak and it not be visible
when the black plastic housing is in place - ie leak into the housing then
find its way out the bottom?

I would thing that if it were the core it would leak when the heater is on
-??

I drove all last summer and this winter with heater on and have had no
leaks.  I would like to attend to the problem as will likely get worse -
whatever it is.  I would like to get educated before I take it to a mechanic
(when I find one).

There are many archives on rear heaters problems.  I have 170,000 km on the
van.  As I will be paying labour should I get the whole thing (core valve
etc) replaced while I am at it - even if it were just an O'ring?

I also saw in archives that you can get air into cooling system from the
rear heater?  I have a coolant level / air problem that will be the subject
of another post "Coolant loss in expansion tank but not fill tank" perhaps
there is a connection?

Thanks for any input...

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