I just had a rear glass installed in my 450slc. I removed it because of rust around the hole for the defroster wire.
The shop that installed it assured me that they knew how to do it. Well, they didn't. They slathered so much lubricant on the seal that now the metal trim won't stay in the slot. Without the trim not only does the window look bad but the upper corners don't follow the contour of the frame. They blame the fact that the trim doesn't stay on the fact that I bent it taking it out. The trim is so soft that it can easily be installed regardless of how bent it is. In fact the trim is not bent at all but of course they are looking for any excuse. I am going to take it back again but I doubt that they can fix it since they couldn't get it right the first time.
Your trick with the rope sounds like a great idea.