Could be this, but you’d have to take your camera apart to find out. If you do, let me know. The fact that your haze developed over time is interesting, and gives weight to my theory that it relates to the oil they seem to be using on the lens threads. (This whole thread may be interesting to you. )
I haven’t taken apart a Cam Pan, so I don’t know for sure what the lens/sensor would look like inside. But if it’s a simlar setup, it makes sense that you might be seeing something similar.