Oki C5800 prints magenta streaks

Your getting Magenta (red) or cyan (blue) streaks down the page, chances are that image drum is bad.
You can try cleaning the LED heads in the hood of the printer. little alchol or glass cleaner on a paper towel or rag and wipe them off.
sunlight is an image drums enemy, sunlight will destroy the image drum. more then likely, streaks or dots going down the page is that color image drum, even if they're at +90%..

Streaks can be caused by a number of things
The fuser
The ETB
The toner cartridge
The firmware
The printer needs a cleaning.
The slot in the printer.
Incorrect Media.

Try cleaning the printer, use a lint-free cloth for the ETB, DO NOT touch the belt with your fingers, the oil from fingers will often make things worse.
Always use a lint-free cloth, if you ever encounter dirt inside the printer, dampen the cloth.

Calibrate the printer.
From the printer's control panel menu
Configure Device-> Print Quality-> Calibrate now.
(Press the Checkmark key to advance through menus)