Digital BW, The Print

Barry,
You mention checking/replacing the tubes.
They all feel hard to me. How would you replace them - just prying 
them off the cfs cart and sticking replacements on ?

And how would I put Epson carts back in - just lift up the CFS carts 
& plug the bottom ink holes with rivets - that's it ?

And Jim, the specs I omitted that you said are relevant to the 
problem are - I'm in the frigid cold north (Ontario, Canada) and my 
setup is in the basement. It's clean but not hot'n humid. And Lake 
Ontario is probably close to sea level.

Mystery is that after clearing the nozzles, by doing 3 quick 
consecutive head cleanings and letting it stand for a few hours, the 
nozzle check is good and the print/s is fine - but it doesn't last 
long before I see a bad print! And then a nozzle check verifies 
amessed up pattern with missing bars.
Frank