I have a Bursnter, the window needs replacing . I managed to get the old one off as the top left corner was damaged it just slid off the runner. however the new one wont slide on as the hinge/slide is enclosed by the window..
You only managed to slide the old one off as a corner was damaged, otherwise it would not have done so.
To fit the new window you need to get it in approximately the right position and lift it above 90 degrees to the front of the van and clip the window part of the hinge into the rail, then shut the window.