Not sure if this affects the 2.5 engine but a dodgy light switch can cause starting problems I've only seen it on the 1.9 up to now
The switch causes a fault in the off position and the car will take a few turns before it fires but if you put the side lights on it will fire first time
Worth a check seen as though its easy to check and free
My money's on this
Iv not seen this one but will wait for the result as its not ruled out on other VAG cars.