Power Window Problem 87 Vanagon

'87 Vanagon Camper

The passenger side power window won't go down more that 2-3 inches. It
doesn't seem to be the switch as it's the same using with the drivers or
passengers switches (actually it's a button for up and down).

I have taken off the inside cover off the door and greased the guide or
slide so that the window goes up and down manualy but the electric motor
still won't pull it up or down more that a couple of inches.

So my question is:

Is this a problem with the electric motor that drives the window up and
down? or is it the regulator or both?

Are there any diagrams on the net of this? Bentley doesn't do a very
good job of diagraming this.

Are these power window motors or regulators for this model interchangeable
with other VW
products that I might find in the boneyard? e.g Jetta, Golf. etc. or are
these
electric motors repairable?

Any other solutions besides buying something new from the dealer?

Thanks in advance for any assistance

Wray