Over time the printer head gets dirty/messey/ink seepage which dries. The result of which is some debris of the most used ink, usually black, smudges/sticks to printer head and can be laid onto print job in streakes etc.
To fix you need to thoroughly clean the printer head and it's seating. 1. take out all the printer cartridges and cover the ink outflow sop they wont dry. 2. take out printer head and thoroughly wash it with a tooth brush, soap and tap water so it's nice and c lean. Dry it. 3. reassemble - prints good as new. Rolfus