I have DG UPVC windows which seem to have been fitted in a hurry - problem seems to be that some of the frames have been put in and they are very slightly warped causing the seal to not completely make at places. The closing mechanism is a pin which pulls accross and marries into a stay (not sure on correct terminology) pulling the window tight to the frame.
If I had slightly wider stays it would pull the window in as desired, they were originally fitted with the slimmer side out and after flipping them the problem is slightly better - bigger ones would fix this issue I think.
Are these available to buy as i can't seem to source any online and are they available in different sizes (gap size)? Make on them is Roto.
Hope that makes some sense but if you need any clarification then please let me know.