Recived my 5d3 last week and upon inspection I noticed a black spec when looking through the viewfinder with no lens attached. I narrowed it down to a foreign body on the focus screen. No knowing much about the focus screen I tried to blow the object off with no luck. So I got a lint free tissue and gently wiped away the spec and guess what? I know have some more marks when I look through the viewfinder! I did not know how delicate these screens are. I'm off to send it in to a canon repair centre hoping to get it cleaned/replaced under warranty as there should of been no foreign bodies or dirt on the focus screen. Any ideas. Score sending it in. It's not really that bad but I know it's there and you can just see the mark I you get it in the right light. Is there a way to clean I safely without marking it?