Epson R300 intermittent

Specifically, the black head. i have cleaned the head using one of the solutions on the market, and achieved a good nozzle check. after half a page or so of 'normal' printing the printout becomes 'intermittent' and a nozzle check indicates failed nozzles.

However, leave the printer for a while (without cleaning) and a good nozzle check
Seems the ink is slow getting to the print nozzles, which work when they have ink.
I have tried prolonged (2 day) soak in distilled water, and a soak in a very weak solution of ammonia
I have a feeling 'somewhere' on the web I saw mentioned that the feed to the head (little spike that goes into cartridge) can become blocked, requiring a very fine wire (supplied with the kit) to unblock the spike.

Has anyone got any idea what my prob is? anyone heard of this 'fine wire' fix??