Epson R2400 head clog

I don't print very often. Or at least sporadically. My printer remains powered up but I've not used it for a couple of months. Having just replaced 3 carts I'm getting a patchy test output in the sixth (from left) group, corresponding, I would have guessed, to the Light Magenta cart, after several cleaning passes. It's excruciating to see the printer eating ink from the clear channels when attempting to clean a single colour. I'd have thought that just printing out a block of colour from the offending cart would effect the same thing but leave the other carts un-drained. The prospect of throwing away a vast amount of overpriced ink makes me feel quite ill.
Any comments would be appreciated.
Roy