66 Dart GT HT Whatsitgonnabe?
I use the powdered silver one. It adheres when the coolant is warm. I would put a pan under it right now and get it running if it just seeping to see if there are more issues. After the air is out and the coolant is moving put the cap on and let it build pressure, there might be more rad issues that it will not work for. It is designed for pinhole leaks.