so it prints to me I think it must be the development unit there is to change the developer dust

I would say that you see the cylinder blade and the fuser first, in general when it is the developer, the copies come out more than repeated or stains you behind the blade. Discard that first and then go to the developer.

If you use toner of another reference or worse, this brand can happen to another brand.

WATCH FOR CHANGING A GOOD QUALITY FUSER ROLLER ALREADY HAPPENED TO ME WITH A MP171