Hi Kev,
Your car has only 27,000 miles on the clock, and the ZF gearbox is a pretty good piece of engineering, used in Rolls Royce and many other prestige cars. It is supposed to be sealed for life, and unless you feel that there is a problem with the gearbox I would tend to leave it alone. --- and if you have a warranty, all the better.
I had a Rover Sterling 2.5 Litre with the auto gearbox an edit never presented a problem till I sold it after 12 years and 122,000 on the clock --- and I also towed a caravan with without any problem.
The minor niggles the dealer must fix for you to be satisfied.
Regards,
Peter.