After a futile attempt to flush out the clogged PK buffer, I studied the R3000 manual very carefully, bought the ink supply parts from Compass Micro (best price on the market) and switched out the parts. As Dana noted, the process is fairly straightforward, provided you really study the manual.
My newest problem: the Y, VLM, LC and PK seem fine on nozzle checks, although I had to run five head cleanings to bring up the first four; PK was the only one to show up on the initial nozzle check. The M, C, LK and LLK inks have not registered on any nozzle checks. Further, all of the ink lines leading from the cart holder to the head are apparently full of ink. I should add that I'm running a Mac and have yet to add Windows, which is preventing me from buying the power clean set up (think $$$$). I had to temporarily stop with the head cleanings as I'm virtually out of PK.
Did I do something dumb during the switching out process? Is there anything else that I can do short of going to the power clean? I'm currently at a loss as to my next step. My thanks in advance. BTW, switching out the ink supply parts really took me out of my comfort zone; but, I'm grateful for the experience--I learned a lot about my capabilities.