Printer C2665DNF - Streak on Output

When I print something, some of the pages, not all, have a small streak along the left side of the page. Maybe 1/2-1" wide and will either be a small mark, or a long mark and sometimes is mixed with multiple colors. It starts thick then fades out, like there's toner on a roller (it looks like a streak that a roller would start then the ink would just rub off the roller, if that makes sense). Again, it's not on every page, but there's no rhyme or reason to which page it does this on. It's not spearing the ink on the papers/words, etc. It just has this streak on the very left side of the page, starting about the middle or near the bottom half of the page...on the very left.

I've researched different solutions and tried some - I cleaned multiple parts in the printer, however, it's still occurring. The ink drums and toner are all dell brand and are all good on their lives. I am afraid if I buy the Maintenance Kit (Belt Unit 2nd BTR and CST Retard Roller) that I may still have the issue. I just don't want to spend so much money for those 3 things to not be the problem. 

So if anyone else has this experience or knowledge on what I can change or try, please let me know.