Just to add...
There is just three way to get the Red Bull X1 car: Vetter Challenge (lvl 30 to unlock), B-Spec lvl 35 and A-Spec lvl 40 (you can buy it after this lvl).
After that you can use it only in the Endurance races (A or B-Spec) and more one Seasonal Event specific for it.
There is no easy win in GT5... the events are hard even the first.
Edit - There is a new Year End/New Year Seasonal Events (time trial) out today... it's hard for hell... I can't even get broze in the first race.