Just to complicate things: OAT antifreeze is what is recommended for a modern engine mainly made of aluminium - just as the Roadster. As far as I know the Roadster 3l enginge comes from the Ford Mondeo, and if you look that up on the net, OAT is recommended for that specific engine. I do not think matters change when you put it into a Morgan. So what to do? I worried more about the engine block than the rad, so I put in OAT, but of course I do not know what harmful effects could have occured with non-OAT. Comments?
By the way, I had exactly the same problem on my Roadster. Easy fix. Got the rad out, brushed the black paint away around the drain plug to expose brass. It is soft lead soldered, so it took me ten minutes with (a large!) soldering iron and some lead. Has not leaked since. The biggest job was to get the rad in and out. Or more correctly, down and up, as I took it out from below...
