When i start the projector picture is good, but when it works for 5 minutes, the border of the picture become smoked blue... Please someone, help me to solve the problem

I have a sony vpl-cs1 lcd data projector that I have used for 4 years.just after 3rd year I started to get a blue hue spot on picture image. The image could be actually focused in on and looked like some sorta water spot.I have taken projector apart 4 times as far as i could break down lens and cleaned them,but didnt help.I bought a new bulb for $325 and was dismayed 2 discover problem didnt go away. The image is still a crisp clear image ,it just has a blue haze on most of projection now. Over time the hue has grown to most of the image except for top corners(they are still clear and very sharp. Can anyone enlighten me what may be problem?I dont have the $ to replace this toy, and I wonder if its a common problem . I hope I dont need some sorta LED display circuit board or something. THANKS IN ADVANCE