Ah...more than likely your gears are just worn out. You prob have a lot of miles on the car which wears the tiny plastic odometer gears out. Take the whole cluster out and take off the needles, but make sure you take a pic of where the needles were when you took them off, take the gauge plates off to get to the odometer. U'll need a very tiny wrench to get the odometer out and then you will see that plastic gear. You'll prob notice that the teeth are way too worn.
I'm not really sure where you could get one...maybe Ford would be the best? Junkyards will have whole cluster's for sale, but there around 60 bucks. I have a cluster layin around if you absulutley need one.
Hint: after you get it fixed and want to put the cluster back in, I would just plug in both the plugs in the back of the cluster and then once you have the needles on turn the key to the "on" position so you make sure the needles are in the correct spot. Once there in the right spot then you can put the plastic lens back on.
Good luck! Hope this is the problem. It sounds complicated, but once you start tickering with it it's not that hard, just time consuming!