Heater core problem F150

Thank you for all of these comments. I will verify the o-rings. I will ask about installation. I don’t know if dye has been used. Will ask. . Radiator cap not replaced. So if the cap were defective and pressure ran up, it could blow out the core?
So far I have used the dealership and they have been helpful but still trouble. As a second opinion, who would you go to?