Digital BW, The Print

Sorry, I forgot to add (actually, hesitated to add):-

when I was caught out like you (empty chambers due to leaks), I
assumed the printhead had got full of air.  I *gently* syringed some
of the appropriate ink into the nozzle using a spare length of
silicone CIS tube.  This fixed the problem in my case each time. 

I suspect this is a very risky procedure (the risks being damage to
the print head as it is not made to operate under pressure) the value
of my printers was considered unimportant at the time I did this (3
times on 2 printers).

Ken