Digital BW, The Print

I've tried cleaning the black plastic tray which has little 'pockets' 
in it, over which the print head travels. But I am still getting 
small ink stains on the very edge of the paper, particularly on one 
of the trailing corners of the paper as it feeds through. It is 
inconsistent with some prints coming out clean. 

How can i get rid of this pestilence. It's a frustrating waste of 
good prints