Digital BW, The Print

This is a new one for me.

While printing various versions of an image today, I noticed a slow
(from print to print) degradation in the print quality (banding; grayish
blacks)\ufffdespecially in the deepest blacks. I tried several head cleanings
and, that failing, I printed several purge pages trying to get the black
to print. Finally, upon close examination of the CIS and carts, I found
that the vinyl tubing that leads to the black cart had developed a
slight crimp where the tubing is fastened to the cartridge. The crimping
stopped the flow of ink to the cartridge and, slowly, it had
emptied\ufffdtotally. When I pulled the black cartridge out of the printer,
there appeared to be no ink in it at all. I massaged the crimp out of
the tube and ran a couple of more head cleanings. I also elevated the
black ink bottle in order to help force the flow of ink. Finally, after
printing a couple of black-only purge pages the cartridge filled back
up. 

Has anyone else experienced this? I also noticed that the tubing is
hitting the printer casing that hangs over the heads and there is
actually a small wear spot on the tubing leading to the black cartridge.
I'm a little concerned that this might eventually lead to a failure in
the tubing.

This is a nomorecarts cis that I bought in October and have used very
uneventfully til now.
You just never know.

Thanks
Peter Lindman