Hi all.
I, too, have had this recurring problem with the rear seats in my X reg A2. For removal, Maersk's tip is on the money, but for re-inserting the b****rs, well it does seem to be something of a hidden art. I tried and failed with the L-H seat after I'd removed both for cleaning and treating the leather, tried to get the technician to have a go, and he failed, too.
I'd say it is a common problem, since a few have already mentioned it and those feet bottoms do seem very unforgiving in being seated properly in their mounts.
It's now with Wimbledon Audi. Let's see if they do actually fix it this time, since another month will mean that the car is outside its warranty period....
It is also in for a check of the power steering. Hope to god it's nothing serious, but it has intermittently tightened up on a couple of occasions, which is most unsettling whilst last weekend the dashboard display showed an orange image of a steering wheel with an exclamation mark alongside it....
I do hope they have a proper look into it...