Hp 4500 color laserjet

Customer has had the machine for a few years and purchased it new. Ran such a small amount of pages through it using it every few months that the life counters are still at 100%. Here is the problem: the prints have gray streaks on them . Drum and transfer belt both have the streaks on them, I cleaned them both off and both look brand new as they should having been hardly used. But when i put them back in after cleaning the prints look the same if not worse and have the streaks back on them? What should i replace, the drum or transfer assembly? if the drum cleaning blade is bad will that put the streaks onto the transfer belt from drum. Dont know HP color that much so any help appreciated. Thanks in advance.

toner defects?

Take out the Transfer ROLLER, and clean or replace. If The Drum has been in the light for a few minutes it can be bad. Check fuser for junk on the fold out it sometimes collects a lot of toner. Also, wipe off the density sensor in the drum drawer, :)