I had that happen to me on a SP-300v. I let the yellow run to low, didn't heed the warnings! So yellow starting printing magenta as well. I turned off the printer with the heads parked and removed the cover that allows access to the pump and lines. Disconnect the magenta/yellow line from the "Y" going to the pump. use a syringe and carefully and very slowly pull ink through the head. Pull just a tiny tiny amount. put it back together, run a medium or powerful cleaning and test print. Hopefully it got better. If need be repeat or run another cleaning and check if it's improved. Good Luck!!