I've had a 3rd-hand 2011 A7 for the past 3 years, and liked it so much that I'm trading in for another one.
Yes, I have had a couple of gearbox issues during that time; one caused by the electronics, and one by a bursting oil hose. Neither required a new gearbox though.
That might sound like it is fraught with problems, but EVERY car I've had has had it's own unique issue (like a BME5series that needed topping the radiator up every 1000 miles, and often blew holes in the radiator itself!).
I've found the A7 to be a proper "luxury barge", smooth ride, and not as common a sight on the roads as A6/A6/Jag/BMW. I have the petrol 3.0 which has a nice amount of poke in the right range for overtaking on A roads when required.
The trouble with just reviewing the Internet forums, is that most people only visit when they have a problem. The quietness of this forum is a combination of the low numbers of people that drive A7s, and the (realistically) low number of problems.