Door Glass Replacement

[Triton750]

Hi all, I have a 99 2.3 si on 69k miles, my second Galaxy but the first time I've had a problem I can't fathom. I hope someone can help.  A couple of years ago we had a prang which damaged the drivers door.  I picked up an Alhambra door from a local breaker, it came empty, so I had to change all my galaxy parts over to the new door. Problem is, as the glass is lowering it goes through a stiff spot about half way down and the motor sounds strained but it's the best I've managed to set the glass clamps yet.  Same again on the way up. In the past it's gone up the outside of the seal while driving, which triggered the auto drop function, so had to pull over to sort it. That's just one instance from a small list of "AAAAARGH not again" moments which lead me to leaving the door card off until I sort it.
So without any bits of tape or marker pens, my questions; how do I set the glass in the clamps in their correct position? Are there any guide blocks or buffers that can be placed wrong?  I'm pretty sure the mechanism flies up the tracks with no glass in, which is why I assume it's to do with either guide blocks, the mechanism itself out of position or, most likely IMO, the clamps not set right.

I tried wedging the glass in the closed position, then winding the mechanism up to get the clamps in the best place but then found there's no aperture for a screw driver.

Thanks in advance :)