Try cleaning the rivets...some people like to use scothbrite. Once they are clean, putting a small amount of dielectric grease on the rivets. I also have good luck cleaning the coil punger with qtips dipped in alcohol. You do not need new steppers, they just need to be cleaned. The 2nd stepper next the coin unit stepper is the ball count stepper.

Somtimes the pivot points of the steppers get gummed up with old grease. They can be cleaned with brakleen..put a rag under to catch over spray. 3 in 1 can be used to reduce metal on metal friction.