Hi . Ive been having a ongoing problem with my 64s having stripes. they look yellow . or sometimes look like dark advancement marks.

i have changed the lt. magentsa and the mengenta heads . both made a change for a little while maybe 6mths to a year and went right back to doing it .  is there a reason why they didnt last long or maybe a underlying problem. rest of the colors print beautiful just seems to be magenta. i do a print test and all the lines are correct and none are missing. i run onyx could there be a problem there ? . the guy we puchased it from wants me to replace the heads again . but at $2500 a head my boss will hit the roof . also after 6 years the dampers have never been changed .. could that be the issue . thanks