PVC door which can have the top window opened in two ways - problem

[Rollerball]

The back door of my property is a brown PVC type which has a top window that can be opened in two ways depending on the position of the handle - it can either swing down a bit (therefore it hinges horizontally at the base of the window) or it can open in a more conventional manner, therefore it hinges on the right side. (This is all from the point of view of looking from the inside out with the main door hinges on the right).

It's never used though, I just leave it shut.

Intermittently over the years I've had problems keeping the top right corner firmly closed, this is where the main metal bracket mechanism is located - by turning the handle to just the right angle I can get the top right corner to firmly lock but then the bottom left corner isn't firmly closed. As I continue to turn the handle there is then a 'click' as of metal either locking into place or perhaps coming out in the top right corner.

This loose locking in the top right corner means that it rattles as the door is opened or closed.

I can't see a manufacturer's name of the door, I'm also not sure what type of door it is. The door is about 20 years old.

Any thoughts please on how to resolve this? I'm almost tempted to drill some holes and just screw the window shut ......

 

[a.window.part]

It's a tilt & turn window, sounds like either the espag rod or the keeps are gone, a few pictures would really help

 

[Rollerball]

I'll try and get some photos, I can in fact see now what's going wrong but I can't think of a way to easily solve the problem. It's to do with the top keep, the metal it slides into and the way that the door was installed maybe 20 years ago ......