Hello Arturasz
two years ago I had the same issue. I had to exchange the clutch.I refurbish my Gangsteller because a little bit oil was leaking (new custom gasket). Because the gearbox was removed I tock the opportunity and had it refurbished too.
The gearbox was filled with new oil but the car (and the gears) had not been moved. I tried to move the control shaft. It worked fine, but very precisely and tight. The I started Getriebegrundeinstellung. It ran twice and stopped with RTF 12 after the second 28th step.
I started it again, same result. Then a Friend of mine an I looked at the control shaft being driven by the Gangsteller. All the measurement positions of the revers gear the first gear the second, fourth and fifths had been reached. At the end the Gangsteller moved but did not reach the neutral position. Then the procedure started again automaticly for the second run. So the Gangsteller was able to reach the neutral and the again the revers and all other gears. After this second round I could read after step 28 the RTF 12 error message. The solution for me was to announce every step from 1 to 28 to my friend lying under the car watching the Gangsteller and control shaft. After the I guess 4 measurement positions of the 5th gear my frient helps the Gangsteller to reach the neutral position at step 28.(Pushing gently with his finger to the screw that fastens the control shaft to the Gangsteller.) This last movement of the Gangsteller was too weak.
With this the Grundeinstellung tooks only the first 28 steps and did not repeat them for a second time. The program finished normally with the following steps (gas break and tiptronic switch movements).
I would guess there might be a software bug. The last hydraulic valve impulse for leaving the 5th gear (to neutral) is too short for a tight and new refurbished gearbox.
After this Grundeinstellung the A2 drives and switches normally until today (about two years). Hope that might help and save some hours of trying and watching the Grundeinstellung. Have a close lock at all the movements of the control shaft. All the twisting to change the lane and the pulling and pushing to select the even and odd gears. You should be familiar with an ordinary manual gearbox. During the first 27 steps You can judge weather the Gangsteller and gearbox work well. If so a little push at the 28 step might help.
Success Cheers Carsten
