If the metal plate between the 2 white plastic bits keeps rotating during operation it can be fixed by drilling 2x 3mm holes throught tha plastic and metal plate. Fit the assembly and rotate the plate back in place. Take 3mm wire and push it through the holes and tie it together using pliers. Plan before you do this to make sure the wires don't interfere with the operation of the window.


The white plastic bit that slides in the guide is known to break too. I fixed mine by once again drilling 3mm holes through the broken bits. Then used 3mm wire that I 'roughened' with sanding paper, covered in superglue and then pushed through the holes. There are many places on the plastic slider where this can be done.

I performed both these repairs on the same 124 window 3 years ago and it still works perfectly to this day.