Can you scan or take a picture of it to post here?
A good guess, since it applies to not just one of the CMYK from your description is that there is a damaged fuser in play.
Top and right side of the page is't something we can account for remotely.
Does the line travel the direction of the paper going through the printer, or is it at a 90 degree angle to the feed direction?
Best first step is to take out the fuser and have a look at the roller. Just remember it is quite hot.
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for posts that resolve your issues. Your feedback counts!Joe Arseneau