Most of the time I see this, I carefully check the optical path for an unglued polarizer, integrator or diffusion assembly; they often come unglued with age and heat especially considering that particular unit is somewhere around 10 years old. The process for getting to the optical engine is not insignificant. Sometimes a focal lens can shift inside the main lens assembly as well. We've had brand new projectors exhibit this symptom and it's usually due to careless handling in shipment. If the haze you're seeing appears as if it's in the image itself, and is exacerbated by a white background, then it's most likely a heavy dust accumulation on one of the LCD panels (the red one in this case). Again, major surgery.