Audi? Mate, this is an alfa romeo forum and 147 gta is an alfa, not an audi.
Alfa 147 gta are fairly relibale as long as they're maintained properly. The weak points are a water pump( the impeler on the inside needs to be changed from plastic to metal one, otherwise it can crack easily and cause the engine to overheat)
And diff, change to q2 limited slip one and you will have a car that handles better and is more reliable, the standard diff is too weak for the amount of torque v6 makes.
Selespeed unit in gtas is completely diferent to the standard 2.0l in 147, 156 & gts - it shifts gears faster and it is more reliable, but once again it has be maintained properly with full system and clutch calibrations done at least every 6k