Xerox DC260 Colour Fading

I have bought a used Xerox DC260 with New genuine toner and drums. When I was printing a letter head with a small logo on the center of the page, I notified the colour is changing while printing about 750 copies. Then I print a test page with solid CMYK strips and I found that the cyan colour is fading in area where was the logo in that letter head. I'm a new to this machines and needs your help to solve this.