I used this material to cover up bad weld on a GTV, as well as other applications. It comes in a tube about an inch thick There are 2 materials in the tube, you cut a slice and mend it like a puddy. It gets hard as steal, I use it to cover holes like this. Sorry don't know the name of it, but it's always near the JB Weld. Make sure if you use it you get the finish you desire cause it's very hard to sand or flattin'
What you are describing sounds like Mill Putty. I don't think I spelled it correctly.