Help! GMT Master ii broken?

[Manc]

Hi, i have a GMT Master ii which is under 4 years old. It was purchased from new. I only wear it occasionally say twice a month. This weekend when i wound and adjusted it i noticed the hour arm didnt jump cleanly between hours. When i pushed the crown in the hour hand jumped back an hour and it doesnt keep accurate time. Im fearing its not a simple fix but appreciate any advice. This is my first Rolex so not very happy.