Wow, it sounds like you've had a really rough time of it with your shoulder - amazing to have to have 5 surgeries. Hang in there with that. VERY important you get that printer running so you can be distracted from the pain and mess you're dealing with. I know all about it.
So yes, I would recommend you do a purge ink routine. The old ink that's in the lines needs to be purged and head cleanings are the slow way of doing it.
Run the purge ink routine from the front panel, then continue on with your head cleanings.
Re: directions on how to replace the distribution tubes, man, I do not know where to find it, except to check out a 400 page repair manual. Keep working on the head cleanings though. If you're seeing improvement, then you may be getting somewhere. For goodness sakes, be sure to leave the printer running - don't shut it down! ( http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&objectID=c00812090
Do NOT do anything with the ink tubes as they can't have any air in them or it will kill all your printheads over and over again until you purchase setup printheads and purge the air from the tubes - a tricky procedure.
Good luck with it, I think you'll see marked improvement after a purge ink and several more head cleanings. If you don't see more improvement after two more cleaning cycles, run another purge ink cycle. You get the idea. I don't recommend putting anything in a cartridge such as lighter fluid or alcohol, etc., (remedies you see on the net) - just keep working on the head cleanings, I believe you'll get there eventually.
Good luck with your next surgery and best wishes with the shoulder.