Hi luccaspal, sorry for not responding quicker! Whenever dealing with problems, it is always important to consider all the facts to help narrow down and determine the cause/solution to the issue.
You started using ConeColor K2 inks around August 2010 in pre-filled carts, then began switching to the refillable carts in April 2011, with the last refill cart bought in October 2011- so you have been using these inks and refill carts in your printer for well over a year. Based on our email history, I see you first mentioned some magenta blobs on the paper, primarily in the white margin, last April, but in May told me the problem was gone and you were happily printing (other than a chip read error we helped you with between that time, and your recent report of getting darker output after upgrading from Photoshop CS4 or CS6). Since then, you have followed my recommendations for cleaning your printer and have replaced many parts including the dampers, wiper blade, flushing box, capping station and print head (twice, as you said the first one didn't work). You are able to get good prints without the blobs after cleaning, but then the blobs return after making several prints. I can assure you that ConeColor K2 inks have been the same formulation since the beginning, and the inks have not changed at all over the years.
Please open the front cover of your printer and carefully examine the length of ink lines inside- is there air in any of the ink lines (specifically the M or LM that you are experiencing flow problems with), or they all totally filed with ink?
Things that could cause ink dripping from the print head are: 1. damaged, dirty or faulty print head, 2. damper(s) not working correctly or improperly connected to the print head, 3. dirty or poorly connected capping station, flushing box and/or wiper blade (these areas control print head cleaning- if the FB or CS are dirty or have a poor fitting, then will not have proper suction during cleaning cycles. If the wiper blade is dirty, damaged or incorrectly attached- it will not be able to keep the bottom of the print head clean, causing waste ink and paper fibers to build up and form a gunk, which can cause smears and/or drips on the paper during printing). 4. Poor ink flow from a cartridge, 5. very high or low humidity or temperature levels in the printing environment.
If you are only seeing magenta colored ink spots on your paper, and no other colors, then you could certainly try inserting different M + LM carts to check if the problem stops or continues to test and determine if one of the carts is causing the ink to drip. If you don't have any other M and/or LM carts to try, let me know and I will check what I may have here to send you.
Please keep me posted, let me know if you need carts to test, if you have questions, or if there's anything further that I can help you with.
Best regards~ Dana