Stepper motors

[zippy500]

Ive just had my car(Griff 500) tuned up and the notorious stepper motor is sort of playimg up. The lads said it was moving a lot slower than normal. They havent changed it as yet and said see how you get on/come back if it gets worse.
Does anyone know, other than cleaning it, if there is anything you can do to mend them or shall I go and buy another to fit myself.