87 ford fairlane power window

Hello all,
Im Peter from Melb Australia
I have a ford fairlane ZL 1987 model
My problem is the back doors window is not tracking properly, pulls out
an gets stuck.
Was wondering if anyone knows what I need to do to repair it my self
I have pulled it apart once can't see what the problem might be
any advise will be greatly appreciated ..
Cheers :mrgreen:

  ladford