By Jamie Spencer Manchester United have officially welcome Ruud van Nistelrooy back to the club as the former Old Trafford favourite joins Erik ten Hag’s revamped coaching staff. The 48-year-old arrives back in Manchester alongside fellow Dutchman Rene Hake as an assistant manager. Meanwhile, Mitchell van der Gaag has left to pursue his own managerial career, with Benni McCarthy also departing, but Steve McClaren and Darren Fletcher staying. Van Nistelrooy’s time in Manchester as a player felt all too brief, perhaps due to leaving just as Sir Alex Ferguson was building his third great United s…