Thanks for updating the post
Good work, not an easy job.
Just FYI, when I change coolant I back flush my heater core.
I know which heater hose is IN and which is OUT on all my vehicles, IN is the warmer one when heater is ON, I put white tape on IN.
After draining coolant I put garden hose on OUT hose and point IN hose down at the ground, then back flush it
It just cleans out any debris that may have gone IN but can't get OUT because tubes are too small, these blockages can prevent coolant from protecting that area so it starts to corroded and then leak.
Doesn't take long on any vehicle, regular flush is fine, but back flush is better