Back in the early 90's I had a PLP-II printer (kind of a cheap laser printer- it used an LED array instead of a laser), which printed great, but after two years the printing became erratic. I don't recall if the company had a fix for the problem, or it was too expensive, but I found a fix online which involved taking the image transfer assembly apart and (I think) adding a bit of tape somewhere as a spacer, and cleaning the unit of errant toner. The fix had to be done every so often (for me it was about 8 months) and it was a fairly messy job. I kept repairing it until I ran out of toner and bought an HP inkjet. Color was such a novelty!
The interesting thing was that it was repairable; even the electronics were all off the shelf except for the LED array itself. I think I still have the PCBs somewhere.
Anecdotally, I recently attempted to repair an Epson Artisan 837 AIO ink jet printer. I found the complete service manual online. After 9 hours of disassembly, I had it back together and working as before. But I didn’t fix the problem. Printer price ~$300. Age ~4 years. Epson estimated service $300. My time value according to my wife ~$500. My conclusion, buy a new printer, recycle old printer. Do not repeat exercise.