I used to support corporate level HP laser printers, a few thoughts:
First, the vast majority of monochrome print quality problems were related to third party or remanufactured toner. HP does not remanufacture cartridges. I would say 80-90% of print quality problems were not HP cartridges, & the remaining 10-20% that were would have been covered by HP's lifetime toner cartridge warranty (if it fails before it's out of toner, it's replaced).
Second, cartridges are not designed to last forever. They're metal & plastic, & they do have a life expectancy. Gears wear, the OPC ages, the cleaning blade gets scratched & damaged, they simply can't last forever.
Third, I would be extremely wary of DIY kits. If you don't seal the cartridge properly you're just asking for a toner spill. Even "professionally" refilled carts can cause problems, ESPECIALLY if they use external clips to "seal" the cartridge. We saw color laser printers essentially destroyed by metal clips falling off of refilled cartridges & damaging the guts of the toner carousel.
I know $200 seems like a lot for a toner cartridge, but the cost per page is already much, much lower than inkjets. Spend the money, replace the cartridge.
Viper GTS