Should I replace my Heater Core? on 2004 Honda Civic

So my windows started fogging up on my recently, my temp gauges are normal, I see no leaking inside the car anywhere, and the heat and AC work just fine. DO i need to replace my heater core or just have it flushed? Or is it something else entirely?

It should be noted that I have heard a bubbling/gurgling noise for over a year come from behind the dashboard when I turn on/off or at stop but not always consistently. This may or may not be related but you tell me. Thanks!

Asked by for the 2004 Honda Civic
possible air pocket in cooling system...
is that something I should fix or be concerned about?
1 more answer , 1 more comment
if temp gauge are normal, no leak and no smell of coolant inside below the heater core, coolant tank level is normal i would not replace heater core, i would recommend to flush the coolant if not done in 3 yrs.
Okay, thanks but what about the bubbling noise i hear, is that normal?