'92 F150 Digital odo gone haywire

Kind of a long shot, but I know a few of you guys own /owned Ford trucks in the same age-range as mine, so maybe one of you guys has experienced something similiar..

OK- basically, a few months ago I glanced down at the F150's odo, which read 261,8xx. A week later, it read 261,6xx. I figured I probably read it wrong, and the "8" was actually a "3". (The coating or whatever on the inside of the odo "lens" is disintegrating in this area, makes it hard to read during the day.) So anyway, next day I'm actually watching it out of the corner of my eye as it reads 261,699- and proceeds to 261,000 even, rather than 700. Since then, I haven't paid close attention to it, but I know it's done this sort of thing several times when I wasn't looking, and now reads 264 thousand and some-odd, when my rough calculations place the actual mileage around 268 to 270K. This ringing a bell with anybody? Can it be fixed without a big hassle/expense?