Help with DesignJet30 printheads/cartridges need replacement?

Printing with this printer for an extended period of time (8 years_WinXP/7) is still at very good level. Recently, it begins to have a problem with stripes and omission colors when printing on plain or coated paper. However, in the best mode on photo paper, it does not show yet. According to hw indicators while the last printheads used only 5-25% and cartridges to about 35%. Can we believe it? Driver report shown end of warranty on the head two years ago and cartridges for one year. Does it replace everything (even before the ink consumed?). I would appreciate any advice on this topic, also experience with alternative inks.
Peter