YIKES! Have you removed the PK and M refill carts from your printer and checked them? Have you manually cleaned your printer's capping station, wiper blade and/or bottom of the print head? If not, instructions can be found here: http://www.inkjetmall.com/tech/content.php?133-Printer-Cleaning-and-Preventative-Maintenance
The cartridges are pressurized by the printer to get ink flowing to the head. I would think if a cartridge was damaged and leaking, it would be leaking from the cartridge chamber and not the print head. Leaking from the print head would be caused by a dirty or damaged print head or damper, or excessive pressure on the carts- but the printer pressurizes all carts equally, starting from one side (the left I believe).
About how old is this printer? Magenta is often the first to show signs of restricted ink flow due to build up in the dampers, which is an indication that your printer is older and needs the dampers/ink selector unit replaced.
Please let me know, thanks~ Dana