UPVC door 'barn door window' not closing fully, need a new part?

[Rollerball]

One of my UPVC doors is over 20 years old, for years it's had a problem where the upper 'barn door window' doesn't 100% stay fully closed in one upper corner. The door also faces south and flexes a little in the heat of the sun which means that the severity of the problem varies.

It's the type of door where the upper 'barn door window' can be opened normally ('hinge' on the right), or tilted vertically (so it's effectively hinged at the bottom) depending on the position of the upper handle.

The problem is that when the handle is turned to lock the window in position you hear a 'snap' sound, and I can see what's happening .......... as follows:

The cylindrical sliding piece that sticks up is supposed to engage with a short horizontal strip of metal above it, but it's slipping out of that as the handle is turned and the cylindrical piece slides along it. If the cylindrical piece was just a couple of mm higher it would be fine. Can the cylindrical sliding piece be replaced with something the same but a bit taller, or can anyone else think of a better solution please?

See the image below of the top of the door - the cylindrical sliding piece that I'd referring to is circled in red, the piece of metal that it engages with is circled in yellow:

 

[crank39]

Thats essentially a upvc stable door, the top opener is really a small tilt n turn window, there are many variations of hinges and mechanisms on a tilt n turn window so I can't exactly be sure but generally there is a hinge in the bottom corner and on yours will be bottom right, easily adjustable up or down with a suitable allen key, yours might be slightly different but heres a quick video, or maybe a picture of your hinge from open and closed

 

[Rollerball]

Thanks a lot, that's very helpful - I'll study that and have another look tomorrow and report back here.

 

[Rollerball]

Thats essentially a upvc stable door, the top opener is really a small tilt n turn window, there are many variations of hinges and mechanisms on a tilt n turn window so I can't exactly be sure but generally there is a hinge in the bottom corner and on yours will be bottom right, easily adjustable up or down with a suitable allen key, yours might be slightly different but heres a quick video, or maybe a picture of your hinge from open and closed

Just to say - it worked! Thanks a lot, that's been bugging me on and off for years.