There is really no way to repair the spare tire mechinism. They rust up and sieze do to the location on the van. I personally attempted to pry the cable down on a vehicle about 5 years ago, and finally got the wheel to come down, however after prying and beating the wheel off, the mechinism never worked after that.
You will need a hacksaw blade or a diegrinder and cut the plastic retainer at the center of the wheel. Then you can get at the bolts, to replace the unit.
I hope this helped if so an accept is appreciated