Rear Window Leaking or Removal
 

I've got a 2000 GMC Sierra 3 Door Extended cab. Some gangster tried to "remove" the rear window (and the side ones). The side ones were an intuitive repair. However, the rear one now leaks (a lot- If this was a boat, I'd be lookin' at the fishes.) The trim around it has a couple of cracks. For the time being, I used electrician's duct seal (a stay-soft putty) around the frame. Now it only kinda-sorta leaks. Does anyone know how to remove the assembly so that I may take it to a glass shop for proper rebuilding? <Or purchase a junk yard replacement> It is a three panel window. The center one slides. it is 100% manual and there is no defroster. The local Auto-Glass shops want nothing to do with it. (Rather odd, considering this is the Motor City!) The leak shows up at the top of the frame's perimeter in the same spot on each side- about even with the factory seam in the outer trim.
Thank you for your help!