I've just flushed with PiezoFlush, replaced the dampers and performed a print head scrub on my 7880, clearing the completely blocked M channel and saving the cost of a new print head (with is what the local service company suggested). Happy with that!
While I was working, I came up with this idea to prevent ink from getting into the paper path while the supply lines to the head are disconnected.
Cut a piece of thin plastic to the width of a sheet of A4 paper (or as wide as you want), and about 24-30 inches in length. I used a white bin liner, because the plastic is super thin – and white. Tape a sheet of A4 paper (or as wide as your plastic) to one end. With the Pressure Lever in the released position, feed the paper right through the paper path so it draws the plastic through. Tape the top of the plastic above the paper feed path to hold it in place; the A4 paper should be hanging below the bottom of the printer.
You can now easily see and clean up any spillage while you're working, and you can still perform a head scrub; the plastic is so thin that it doesn't contact the print head.
Clean up any ink you see on the plastic before you remove it, to prevent accidental transfer inside the paper path.