Just an update for future reference if someone is looking for an answer on a similar problem...
it was the Water Pump. Congratulations to all the correct guesses
I finally took it into Footo to get my leaks sorted out once and for all - what I thought might have been a rear main seal turned out to be an Oil Filter Elbow Oring, and what I thought might have been a Head Gasket turned out to be a Water Pump - pretty happy when the total turned out to be about a third of what I thought it could have been
I know its not news to many brisbane-ites on here but a big +1 for FootoMotor - My first time but Peter seems like a great guy and really knows his way around in XJ