Chaps,
Mystery solved...
It was indeed the EGR Hose #4932545.
So called because it runs from the EGR housing down to the cabin heater matrix.
Hard to fathom how it could pin hole on the elbow as it's made of rigid plastic.
Before it finally blew out, the pin hole must have been like a fine hairspray mist for ages,
which was instantly evaporated away by the hot catalytic converter and exhaust directly below it.
So you would get a mysterious coolant leak without ever knowing why...
The only tell-tale clue is the faint smell of coolant...and if you were running a low level of coolant
to water mix, that smell would be hardly detectable!
Worth knowing and looking out for as the elbow is just out of site at the rear (of the transverse) engine!
Best,
Andy M