Streaks on paper

Nisha... If you haven't done so already, you need to run a few copies off the glass as opposed to through the feeder to determine "where" your problem is.
Do the copies of your originals placed on the glass have the same line/streak defects as the ones made run through the feeder?

IF NOT, then you probably have some sort of dirt or contamination on the FAR RIGHT side of the glass (ink, white-out, dirt, etc), and the machine is reading that as part of the image and printing it as a line. When running copies through the feeder, the scanner moves to the far right and parks there. Then the feeder moves the original over the scanner on the right side of the glass (the scanner stays still). So if you find the lines evident when using the feeder, but not there when copying off the glass, you need to clean the glass on the far right.

IF YES (lines/streaks through the feeder AND off the glass), then your problem is most likely internal of the machine (bad drum in the L50 cartridge, dirty optical scanner, worn fuser rollers, etc) and I hate to say it, but will probably require a service call to rectify it.

Sometimes you can actually take the L50 cartridge out immediately after running a few copies, and while holding it up, manually open the spring-loaded drum shutter on the under-side of the cartridge to expose the drum and visually inspect it to see if the line defects on your copies are evident on the drum itself. If so, you will most likely need to simply replace your cartridge and hopefully save a service call.
If you can't really tell if the streaks are on the drum itself, then you're back to probably needing a service call.

NOTE:
DO NOT TOUCH, WIPE, CLEAN, OR OTHERWISE CONTAMINATE THE DRUM WHILE YOU ARE DOING THIS, and do not leave the unit exposed to light for longer than a minute or so, because if the problem isn't evident/obvious with the drum cartridge, you don't want to risk damaging/contaminating it and thereby causing one.

Please let me know if any of this was helpful. Thanks.