So, rather than let the thread die with no updates I'll let you know what happened.
I was using a new steel line section from the rad to a compression fitting on the existing line which was in good shape other than where it broke at the rad fitting.
I carefully had measured and bent the replacement line to what I had taken off, connected it to the compression fitting and then into the rad (which is where my leak was, around the tube and nut).
So I went this AM and got a section of NiCopp 5/16 line 'cause it bends easier and figured I could line up the angle of the line into the rad better and get a better seal.
While it was apart I figured I'd try and put a stub section of line in the rad for a reference point and found out WHEN THE NUT WAS FULLY TIGHT, THE TUBE WAS STILL ABLE TO MOVE!
Turns out as this rad was older stock that sat around there was corrosion around the cone seat and the last few threads that would make the fitting seem like it was fully seated and tight, when in fact the tubing wasn't seated fully before the nut stopped.
Kroil, fine thread chasers and a few cups of coffee later we got it all back together, test drive and no leaks
Just one of those stupid deals where you think new parts are always perfect (even if they're old, new parts).
Moral of the story, check the little things. Nobody like to be known for their motto " We do it nice 'cause we do it twice"
