Yep, thanks for all your advice!

I compared the options and decided to do the rebuild. Found very professional firm to do it, and I will get a 12 months warranty from there for the rebuilt box.

The A8 parts had a spare gear box, but with the needed ECU device and the shipping to Finland + the work removing the old one + fitting the new one would have been very close to the costs of the rebuild. So I decided to fix it. Atleast I should have now clean and working gear box for the next 12 months

The costs will be around 2500 - 3000 euros (in Finland). They said also that it's the clutch, and it wouldn't be too hard to replace but it is needed to take apart and clean + maintenance the whole gear box since otherwise there might be some crap from the broken clutch which would cause damage.

By the way, someone mentioned that the gear box is reseted by pushing the kick-down button under the accelerator for 30 seconds before starting the car? Is this right?

In my Audi the kick-down function doesn't work when you use the tiptronic function, can I fix this by adjusting the switch? Have someone done it?