Today my printer (Epson SC-P800) started to leave green dirt on 4x6 prints (I did not try another size of paper except A4 only for head and paper guide cleaning). I print regularly for the last month and I printed yesterday some 5x7 sheets, and today's first three 4x6 sheets come out perfectly. Then I started noticing small amount of this greeny dirt and at the same time noticed 'low ink' warning for LK.
I decided to print some more sheets wondering "what is this dirt?"... And as it still was on prints I decided to change LK and changed to a new cartridge. However, this did not help. After printing couple more 4x6s, I ran head cleaning and paper guide cleaning but this did not help either. Already printed about 5 sheets and dirt is still there.