Does my heater core need replaced or just back flushed

What is your question?

Symptoms of a heater core going out in my 2001 F150 yet the engine is staying cool and the cabin is staying warm. The symptoms are on and off I could go one day and I have a bit of trouble no leaks yet the very next day it could be leaking like a sift Windows fogging up and some leaking inside the cabin. I have tried to search for the main access point of the leakage and I have failed to find it but when it does leak it leaks good. I am going to bypass the heater core in tirely until I could find the source of the problem thanks for any help that is giving

What makes this problem better or worse?

Seems to be worse when the engine is cold

How long has your 2001 Ford F-150 had this problem?

About a week and a half it's been on and off