1320c streaking down left side even after replacing PHD

I have a DELL 1320c color laser printer about 2-3 years old. A month or so ago it started printing black and cyan colors lighter down the left side of the page.  A light streak about 2 inches wide. Magenta is also a slightly lighter in the same spot but not as bad as black or cyan, which are very obvious. Yellow seems unaffected.

I read the DELL online help for the printer and it said this issue was most likely due to a worn out Print Head Device and that they need replacing every 20,000 copies. So I ordered in a new PHD and replaced it exactly as per the instructions.  But the issue is unchanged! Even with a brand new PHD it prints black and cyan lighter for the left 2 inches from top to bottom on the page, exactly like the old PHD.  The PHD cost me only less than the price of a new printer!

I've also tried swapping out the toner cartridges with new ones. Still no change.  The toner doesn't rub off, so I can't see this being a fuser issue.

Does anyone have any ideas about what could be causing this issue?  The help documentation doesn't give any other possible causes.