Jack, rule of thumb is typically replace the dampers and capping station first which can help dictate what the problem is and what needs to be replaced. If you haven't changed the dampers in some time, it could be an easy fix. When I was referring to the needles and tubes being gunked up, I am referring to the needle that pierces the cartridge which draw ink from the cartridge through the lines and dampers, into the head.
What do you mean when you say the damper didn't come with tubes attached? Dampers should come by themselves and you would need a jig or need to remove the lines from the damper the proper way to not make a mess and you would change them yourself. If you have not done this before, it may be wise to get a technician to do so as you don't want to cause a bigger problem if it is a simple fix. Feel free to give me a call or drop me an email directly as it is sometimes hard communicating on these forums.