DELL 3115CN problem with printing

I have problem with my Dell 3115CN.
The printer is 5 years old, bus was printing quite well so far!
Until last week, when it started to print stripe on the one side of the paper where the colours are different / vanished (please see the scan bellow).

Consumables status is OK:
Fuser    60 %   
Belt Unit    60 %
Cyan Cartridge Level ~ 100 %   
Magenta Cartridge Level ~ 60 %   
Yellow Cartridge Level ~ 80 %   
Black Cartridge Level ~ 30 %   

Any advice to fix the problem?