Try removing the wiper arm and verify the shaft is not turning. There is a small coller that fits on the shaft and then the wiper arm attaches to it. te coller may be loose. If this is not the problem then the wiper motor will need to be replaced. I am not sure how to access it but I tink you may be able to get at it by pulling the fridge them looking up.
1997 2400 SCR
5.7 Vortec / Bravo 2