Sometimes tightening the LCD clamp by a tiny amount - to increase its pressure on the connector strip - will work. Sometimes cleaning the strip (but NOT! the LCD contacts) will work.
Easy to lose the 3 loose switch parts for the illuminator or reverse them, easy to damage the circuit connector (which is thin film) if you don't know what you're doing. It's crucial that you don't mix up the screws - the short csk must go back where it came from.
There used to be a (US I think) company that advertised a restorative liquid for connector strips but I never tried it so don't know if it works or is still available.
If Nikon service is too expensive and if they will supply the parts ask if the connector strip comes with the LCD, you need both.