Digital BW, The Print

Epson 9000, Selenium Inkset w/black-black, Image Print.

I keep getting what I think is a clog in the black position only. If
I do a nozzle check I 
can see it, do a few standard clean cycles, it clears and nozzle
check looks good. Start 
a print and about 1/4 way into it, the black stops again. Do a nozzle
check and it's 
back to a problem.

I have tried the usual Windex, Fantastic cleaning thing, ran a
cleaning cart until ran 
clear, replaced damper, many KK2 cleanings, replaced cart with new
one, did cap 
alignment, etc.

Is it possible that some settling in the black-black cart has gotten
through and has 
damaged the nozzle?

Mark