Hi Mattc,
I have had the same problem with my SP540v on a few occasions. Soaking doesn't always give the desired result. I trick I was shown (and it has worked for me in the past) is to put some Roland cleaning fluid into a syringe and force it through the head via the ink feed tube a few times after you've done the soak routine. You can do this without removing the head, by moving the head carriage to the left a bit , away from the capping stations, and putting some absorbent material/tissues etc under the head)Then, move the head carriage back over the capping stations and wind them up firm against the heads. Leaving the ink drain tube attached to the underside of the Black/Bluecapping station, remove the other end from the pump and attach it to your syringe and use it as a 'vacuum pump'. This will suck/draw fresh Black&Blue ink through the head.
Its uses some ink but it's a lot cheaper than a new head. Failing this, I think that 'artbot' has the answer. I've had to go that way too a couple of times as the test pattern detiorated.
