You need the oil can to oil the gears.
Go to Rock Ridge and recover the missing calf for the cowgirl. She will give you an old saddle. Swap it at the Trading Post in Dusty Gulch (you can also swap for a gold pan, use it, and then swap the pan for the can). Climb up inside the clock tower and oil only the center row of gears until they are all shiny (you should have just enough oil). Turn the crank to get the gears moving again.
Diamond plains
in diamond plains
go to the train station
You oil it.
it is located at the diamond plains
The clock tower is in Diamond Plains, to the right of the section with the marshal's office and the saloon.
After you oil the clock gears the clock will strike 3:00.
the gears in the clock tower
You go out the way you came in, just reverse
The oil can is used to oil the gears of the clock in the clock tower at Diamond Plains, so that the clock will work again.
the clock is in the tower. if you go all the way to your right they are doing construction and if you go inside theres the clock!
just play the game and you will find out.;)