Have you tried doing a calibration? Something is probably dirty and those dirt marks are being carried along with the scanning head. Is there any way to open it up and blow or brush it off? If so you'll want to calibrate after cleaning, not before.
Here at least the 9000F with 9600 DPI scanning is $250 so I wonder if it would be worth repairing a 2 year old model? A shop might give it a cleaning for you for a reasonable amount, worth a try but I'm not in the UK so I can't suggest any locations.