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Thank you to itfc,chas2008 and pauln90 very similar answers by all three.Have taken your advice and it seems to be working so far.The leak was not at the point where I had uncoupled and replaced the radiator but at the flow valve which had a slotted screw head. This I had screwed down as a precaution prior to uncoupling and it was when I UNSCREWED the valve that I discovered the leak There is a chromium dome shape cap that fits over the valve as a decoration/protection which is hand tightened. I am going to tape the thread and tighten with grips.Thank you again
NONREV.