I read this thread because I also had a coolant drip, but it was under the left hand side of the radiator.

There is a small weak point in the radiator design in that an 'O' ring in a the mounting of a small spiggot on the top of the radiator can start to leak. I suspect quite a few owners have replaced their radiators because they could not find a small spare part or the source of the leak-

Mattmog put me on to the solution, and then I found a reference which gave us the part number on, of al places, a Ukrainian forum.

Here is the photo of the part, showing the part number, that Mattmog purchased.

[Linked Image]

I carry a spare in the Morgan just in case I get a failure on a trip.

I mention it here because, although the source of the leak is different, someone might find this thread while searching for a solution.