There's always the question about whether to throw good money at trying to fix something uncertain like this. It's odd that seven of eight nozzles are good in the check but fewer in the ink sep pattern. I agree with Walker that the ink dampers are likely to be the cause, and these could be replaced at modest cost if you do it yourself. But it's a gamble of time and money and there's still those three magenta nozzles that may or may not clear.