To follow up with the response I just posted to your other thread, dampers should be replaced as a set every 1-3 years (you mentioned in the other thread, that only the yellow damper was replaced).
Please remove the M and LM refill carts from your printer and examine them- does ink leak out of the exit valve on it's own? I see you purchased these refillable carts in Oct 2011, so I assume you have been having success with them until recently experiencing missing colors and magenta blobs- is this correct?
Have you ever replaced the flushing box in this printer (in the other thread, you said the pump cap assembly, wiper blade, print head and Y damper were recently replaced).
Please let me know so I can help, thanks- Dana