Simple procedure but Alfa techies sucks!
Just a piece of feedback - I changed this weekend my gearbox oil (I have 159 tbi). Overall, a very simple procedure.
Filler plug can be undone without removing the batter. You just need an extension. It is 8mm allen (AFAIK). Then, undo the drain plug. This is 10mm allen.
WARNING: despite the fact that the manual states 2 liter capacity for the Tbi gearbox, I drained nearly 2.6 liters. I replaced the same amount with the Red Line MT-90 75W90 GL-4 gearbox oil.
I used a black silicone on the drain plug and tightened it to 17 Nm. Looks and feels flush. No oil drips.
Drained oil was dark, but still reddish (car has only 59k km on the clock, 4 years old).
After the change, I have impression that gear changes are smoother. On the capacity issue, Alfa has fu**ed up again. I have no idea what kind of the brainless idiot prepared the manual for the 159 Tbi, because getting gearbox and engine oil capacities wrong in the same manual is beyond a simple "typo"...