The fuser in your laser printer heats and bonds the toner to the paper. It ages over time and can be the cause of print issues (weird streaking on the page, faint print). You can purchase a fuser separately for some printers, for other it comes in a maintenance kit. It can be installed by a printer technician, or you can do it if you’re technically savvy. There are many Youtube videos of fusers being installed on different printer models that are easy to follow.