O/D light blinking

[Spiers]

Im looking at a 2002 Explorer for sale. Looking to get it cheap, fix, and re-sell. The current owner says that the problem is random and seems to happen more often recently. Sometimes it will drive fine, other times, it will be driving down the road, and the O/D OFF light will start flashing, and the transmission will downshift out of overdrive. He says you can pull over, shut the vehicle off. Then start it back up and it will drive fine, until it does it again. He says sometimes it will act up everyday, and other times it will go a few days without trouble.

I am fairly mechanically inclined. What am I looking at to fix the problem?

Also the starter seems to act up from time to time, occasionally wont start unless you tap on the starter. Im guessing a new starter would do the trick on that one.

 

[NHarris]

I bet its the servo pistons. Check out this thread:
5R55W servo piston removal

 

[KPPCExplorer]

I know in my fire department, one of our E350 ambulances was just having this problem. It would start flashing at highway speeds, about the point when OD should be kicking in, and would continue to shift in/out of OD in 1/2 second intervals, making the ride very boggy-like. Changed the tranny fluid several times, and that didn't fix it. Took it to a local tranny shop who said they fixed it, but didn't really. Had to end up bringing it to Ford and have it completely rebuilt, and it drives like a dream now.
Not saying the tranny needs to be rebuilt, just speaking from experience with another Ford.