Hi Paul.
I just wonder if you're trying to fit the chrome trim correctly. The whole width of the trim doesn't need to be pressed inside the groove in the runbber. The edge of the trim which will be closest to the glass side goes into the groove in the rubber and kind of grips and stays there whilst the other edge of the trim which will be closest to the bodywork when the window is fitted, just sits on top of the rubber. Because of the shape of the trim it then all sits down level and looks good. It will be even more tightly gripped once you get the glass back into the car. Don't forget to fit the trim joining strip over the two open ends before you refit the window. I found that the joining strip was actually the hardest bit to fit but if you get it in over one end of the trim you can then slide it along to cover the gap between the two ends. Don't forget that the join in the trim should be on the vertical side of the window where its against the 'B' pillar of the door frame.
Where I did need to open up the groove in the rubber I used the pointed end of one half of a plastic clothes peg.
Good luck!
RoRoVw wrote: