Quarter light window

Hi

This has probably already been asked but i have already tried the search engine to no avail

I want to replace the quarter light seal which I think I'm ok with.
However the my question is what is suppose to hold/seal the glass into the frame.
Mine looks like it has leaked and the po has used solder or something in between the glass and the frame to block leaks.
I know there is a vertical seal, and one that goes round the outline of the opening, but Am I missing something inside the actual frame that moves?

I hope this makes sense

 

Does it open, or is it fixed?

 

opens

 

Is there a seal of some kind between the glass and the aluminum frame? If so any ideas where i can get it from please?

Anyone any ideas ?