Posting a sample would help. The most common causes of print streaks on color laser printers is a defect on the transfer belt or a defective cartridge. If the streak is predominately a single color, then removing the cartridge that matches that color and checking for excess can confirm that. If the streaks are muddy colored, then a problem with either the transfer belt or the secondary transfer roller are the likely cause. Examine both components to see if there is excess toner there. An overfilled waste toner bin can cause toner to backup up onto the transfer belt.
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