Canon FAX L-120 Plain Paper Laser "patchy print" Questions

patchy white line goes down the left hand side of the printed page which makes that section of the page hard to read. It looks like it is the side on which the roller sits. Could someone pleasehelp me

...print quality is patchy. Please help??!! Hello, I'm not familiar with this unit. Make sure you are using the original cartridges and not "compatibles." They claim to be the same but they are not. ...