I ended up doing silicone ,
It worked quite well. It was a little tricky to get it in the right spot and clean off the excess neatly at the same time but the end result is really good

Yeah I think silicone is what I will end up doing. Ill let you know my results when I'm done

Seriously, all I did was tip the glass upside down, put it gently in a bench vise. Ran some good quality silicone down the channel and pressed it on top and let it dry.

I seem to remember holding the glass, and tapping the channel on with a rubber mallet ...

Ditch the rubber and bead the channel with silicone. Set the glass in and wait till cured. Thats what i did, bobs your uncle

Hmm okay I'll persevere, the glass fits fine in the channel without the rubber and has a small gap either side where the rubber would fit,
Maybe I should move onto another job for a bit and come back to this I think

Perhaps the Channel is made wrong. Try it without the rubber glazing. If it won't fit, the channel is too narrow. You might be able to bend it/pry it open wider

I only had mine apart once, and I cannot recall if the glazing was laid in there u-shaped, or cut into two strips. It was very hard to get the glass back in. Steady pressure is what I remember (no hammer)

Maybe I'm doing it wrong, do you fold the rubber over the bottom edge of the window and press it in, or do I cut it in half and put a piece each side?

Yeah this really isn't working for me.
Any other advice?