Did a lens change outside and got a bit of crud into the focusing screen. This didnt affect the photos so I left it be for a month or so. While at a friends home he was cleaning his camera with a air bulb so I asked if he would do mine to only find out it was welded in place so he used a Q tip and canon optic cleaner to get it loose. WELL the lil hair thingy was gone but now the focus screen is full of minor smudges. I said Oh well I can live with it. BUT 10 shots latter and AF not working very well and smudges on the photos I got to get this fixed or buy a new camera. So I read about sensor cleaning ,blow off the sensor and it fixes the smudges on the photos Also read a warning to never touch the screen ( TOO LATE ) my bad. Anyway the viewfinder is full of smudge marks and AF acts real kooky Its hard to get a confirm beep and the lens will hunt for focus a lot . A good cleaning of the chamber, mirror box, and sensor are a must at this point. Can the screen be cleaned or do I need to replace it?