I've had my XBR 950 70" unit since 2005. It's been a beautiful set and have watched countless hours of material on it. Recently the picture seems to be darkening and this is after a brand new bulb has been installed. When Sony replaced my optical block a few years ago, the picture looks absolutely perfect, just recently has the darkness returned. The tech that came out suggested I remove the back panel of the TV at least once every six months and clean out the unit for dust.... but I have yet to do it. I think I'm about to try. What parts should I clean? Are there mirrors or lenses in there that need to be cleaned? I've already cleaned the little optical thing in front of the bulb. Thanks in advance.