4X4 Problems

My Uk Spec 99 Blazer has dropped into 4 wheel drive by itself. The lights on the switch come on briefly from cold and then go out. No amount of button pushing seems to do anything. I have noticed a small amount of fluid on the drive, could this have anything to do with the problem.
Thanks,Alex

Does it have 3 button selectable 4WD or is there an "Auto" button on the switch?

Hi, yes four button,s. Auto-2hi-4hi-4low.
Thanks for the reply.
Alex