Thread update.
Well I finally found the time to have my gearbox serviced, my car had reached 92k miles.
You can really tell the difference, the gearbox particularly at low speeds shifting between forward and reverse is much smoother and I’d recommend it to anyone whos car has reached the ZF recommendations for a gearbox service.
For those who are interested
I managed to locate a genuine ZF8HP70 sump, together with 8 litres of Lifeguard 8 fluid, the attachment screws and sealing/filling plug on ebay.
I purchased these from onestopgearboxshop of High Wycombe via their ebay store for £239.99 delivered next day (November 2016).
http://www.ebay.co.uk/itm/ZF-8HP70-A...kAAOSwn7JYDdwm
Again I trusted the work to TGM Sport in Fleet who have a full diagnostic computer to communicate with the car in order to read the sump temperatures inline with the service document I previously posted.
Access to diagnostic equipment is essential as the gearbox has very a specific filling process which not everyone will be aware of or be able to measure temperatures.
The work took two hours all in, so not too long a process, and in my eyes good preventative maintenance.