I am having a problem with printing defects on my Phaser 7760. I am getting dark lines every 44mm in all colors in the same hue as whatever is printed. I switched out all of my Imaging Units, new transfer roller, and waste cartridge. I tried different papers with the same result. The lines do not appear in areas that have no toner. Test prints all have the same issue. My OS is actually Mac OS 10.6.8 on an old computer that can't upgrade to a newer OS. My main computer OS 10.14.3 Mojave will no longer support the old driver. I've ordered more imaging units and a belt cleaner assembly. The toner is Xerox brand. The only thing I haven't replaced is the fuser and belt cleaner. Thanks in advance.