Black marks on EVERY page - Dell 3115cn

I get a series of black marks approx. 2 inches in from the left side of the (letter sized) paper. It happens on EVERY page I print, whether or not I am printing black, colors, text, pictures, etc. I installed a Dell fuser/transfer belt kit about a year ago and a new black toner cartridge - all Dell OEM parts ordered from Dell - and the problem started happening soon thereafter.

The marks are identical and are always on the same vertical plane. Their position on the pages varies horizontally, though. In other words, the marks are always approx. 2 inches from the left side but move up and down the page as I print. There are 3 to 4 marks on each page, spaced about 2 inches apart. See attached PDF for an example.

Following some troubleshooting instructions found on the Dell support site, I performed a 'stop print' and subsequently eliminated the fuser as a possible culprit. Bearing in mind I do not have a spare belt or black toner cart laying around, I can't simply swap them out to see if the problem goes away. Since the transfer belt is only a year old and the toner has 80% life left, I'm not inclined to rush out and buy new ones on a lark.

Any advice/suggestions are greatly appreciated !

THANKS !!!

RockoC