How do I repair/replace my Printhead?

My printer is leaving white streaks in the black ink portion on each printout that I do and It is getting progressively worse almost as if the ink is drying up. I looked at the upper and lower ink ports where the black ink cartridge fits and the upper one does seem to be dry. Perhaps it is clogged up? If so, how do I disassemble the printhead in order to repair it?

Does anyone know where I can get a repair manual for the HP C8180 All-In-One printer? I have an owner’s manual -I need a repair manual.

The other alternative would be to replace the printhead. There again, I would need to know how to do that as well as needing a repair manual. Can someone show me how to do that?

Then, the last thing, I would need a new printhead. Where do I get one?

Hope someone can help guide me. Thanks.

P.S. I have tried all the self cleaning and print alignment solutions available to me several times and the problem just seems to be getting worse with each successive printout try. I have even replaced the black ink cartridge twice. It is as if the black ink is drying up with each printout try.