Vauxhall Astra 2010 automatic gearbox problems

[Morlandman]

I am the second owner of a 1.6 Astra, purchased in 2013, the car has now covered 52,000 miles. In May 2016 I noticed the coolant level dropping, but could not find a leak. My local Vauxhall garage informed me that there was a re-call for a wiring mod on the coolant system. I asked them to perform a coolant pressure check. They diagnosed the radiator had leaked coolant into the automatic gearbox. I agreed to have the radiator changed for a genuine part, this was completed. January this year the (2017) the transmission failed completely. The car was towed to my local dealer, after spending £100 the results were inconclusive, they then wanted £200 to investigate further, I declined. The car has now been taken to expert who says there was still water in the transmission oil.
On checking the invoice the garage only drained the oil, and refilled with new. This process did not get rid of all of the water, and I conclude it led to the early failure of the gearbox. I contacted Vauxhall customer service by letter, they have failed to offer any help!