A3 gearbox problem?

[kd5]

I have my car (a3 2007) for almost a year (under warranty) and during the first months, occasionally, when I engaged the first gear, there were times that it would go back to neutral while starting driving. Unfortunately, I did not pay much attention to that since I assumed it happened because the car was new.
During the last two months or more, there are times that while accelerating from second gear after a slight maneuver - to overtake or after a roundabout - (always occurs when moving to the left - I live in Greece), the third gear is not possible to engage at all for a moment or so. I have been trying to engage it twice or three times from neutral and was not possible. After a while however it does engage again. I should mention that the second and the fourth gears can be engaged at that time. Do you have any idea what the problem could be?
I am suspecting the gearbox. But since that occurs rarely and has not occured at a mechanic at the service, they say that it has nothing, which is not the case. I am very frustrated about it because I drive at the national road every day (doing 80km per day) to go at work and this brought me on two very dangerous situations. It has occured about 12 times since I have realized it was a problem and it was not me not fully pressing the clutch. It happens only when upshifting from 2nd to 3rd, on aproximately 4000 r...
I already have driven around 18000km.

[kd5]

Just to add that the car has never been bumped and has not even a scratch.

Also, the direction towards which the car moves when this occurs is probably irrelevant and misleading.

Regarding service, the first time I took it to service they did not even want to keep it in order to check it out. Therefore, I had to go again.
The second time I took it to the service, after my insistence, they have found a worn-out grommet. Also, they have done the first service (due aproximately at one year / oil change). After that I thought that the car was ok since for many days this did not reoccured. But after five to six days, the same thing happened again. Only this time during my third effort the third gear was engaged (that is better than before). It did not block that much. So, the problem minimized slightly but did not go away....I took it to service and they cannot find anything wrong
Any ideas? It is new car!!!!!!!!
They are driving me mad!!!

[kd5]

I have to say that they have finally changed the gearbox. It took many months and persistance to do so however. Since then, the problem went away. Finally...