On Tue, 26 Jan 2010 01:18:06 +0000, John Rumm
wrote:

For the first time the other day, I encountered a metal to metal cone
fitting (radiator tap to tail) joint that would not stop leaking however
much it was tightened. The surfaces were new, and looked and felt fine,
but still no joy. In the end I had to resort to winding some PTFE round
the thread on the tail such that it flopped over the mating surface when
the joint was assembled.


For the "first time" ???
I take it you mean it was the first time you encountered a leaking one
and not the first time ever ?

You could have used LSX Sealant .