Level 30 a-spec. Spend the next five days of your life grinding the Sebastian Vettel X1 special event to get all golds. Get three of them.
Once you get level 30 a-spec (maybe b-spec idk) you'll unlock it and it's added to the end of the special events menu. As for the 4 hour endurance, you mean in the endurance series races or the Nurburgring 4 hour track?