Epson Aculaser C1600 - clear vertical lines in print

I've had this problem before in the past, but then i was able to fix it by cleaning the print head window.
This time, cleaning the print head window did help some, i had two clear lines in the print and other went away after cleaning. The other, stronger line remains..
I don't know where the problem could be, since epson technical support for this printer says clear vertical lines can be solved by cleaning print head window or replacing the print cartridge(s). Now i don't believe the problem...

Epson Aculaser C1600 - clear vertical lines in print