So i installed the new DCS World patch over my existing game.   
I opened up again and it was telling me i needed to buy the P-51.   
Ok - so then I reinstalled my P-51 and it's back.    
But now whenever I go to a mission with the P-51 it sounds like the starter motor is constantly cranking and I can't start the engine?    
I go to an air start and the prop is just dead.