[V8] heater core?

[Roger Woodbury]

During the fall when we have had chilly days, my '90 V8 sometimes will
develop fog on all the inside windows.  Normally this will begin only on the
windows facing away from the sun, but it will develop throughout the car and
fog all the windows.  Full defroster with high speed fan will not completely
dissipate the fogging unless I crack open both driver's and passenger's side
windows an inch or so.

This doesn't seem to be altered by either the economy mode or the modes
where the a/c compressor can work, so I assume that this has something to do
with the heater core.

I don't smell glycol or antifreeze, although this afternoon I did seem to
think the air smelled a bit more humid than when the weather was warm.

Am I correct in thinking that this is a fail(ed)(ing) heater core?  Any
comments?

TIA,

Roger

P.S.  Have I mentioned lately how much I LOVE my V8?