Well now 650 miles on and no problems with the box. Just a faulty solenoid. It gave the correct resistance reading across the terminals, but the internals were obviously faulty. .
Moral of the story is to get a good enough code reader that reads gearbox codes not just the engine. You can swap solenoids around to see if its that one but you have to put the sump back and fill again with oil.
I did have a code reader that read box codes and cost just over £100 and does SRS and ABS. If you dont have one and go to a garage i could have forked out between £420 and £3000. My local indy wanted £420 for a flush with nothing else.
The solenoid was £75 next day delivery plus the new oil, plus filters and gaskets at market price.
Not everyone is going to get away with as little as that but at least your for warned with info before a garage treats you like a cash cow
Phil is a star with the ZFgearbox and if the box gave up id go to him first although hes over 200 miles away.
I have Storey Wilson's 4Dcan diagnostics software. So should be able to read:
Range Rover : 2006-2012
Range Rover Sport : 2005-2012
Land Rover LR3 : 2005-2009
Land Rover LR4 : 2009-2012
As per http://www.rswsolutions.com/index.php/range-rover-mkiii/mkiii-all-comms?id=540
Only ever tried it on a Disco LR3 TD6 so far.