Ford warns about leaving a PSOM face-down causing some discoloration, and this is an example of that. Silicone grease from the needle movement is seeping into the LCD, causing it to delaminate, like some rear-view mirrors do. The only fix is to replace the display, which only comes in a PSOM assembly. Try to find one with similar mileage, but they're stored on the PC board - not in the LCD. So if the replacement's miles are substantially different, only swap the LCD into your original PSOM.
New odo display ~$90
